I mean, he'd have to have been with the militia a while to build up enough trust to be seriously considered for the SRT.
But moreover, let me tell you what being a Hell Hound is like.
CW: psychological and physical abuse
So one thing I want to make it clear that the Hell Hounds are basically an incel cult without the weird gender-sexual overtones. I imagine there ARE women and enbies who join it but in essence Andros Capella is a creepy weirdo who preys on disaffected, primarily male youth with no prospects and indoctrinates them into his worldview of nihilistic violence.
Andros doesn't really have a philosophy, or at least not one that he could describe in words (and even if he could, he wouldn't), but it could be summed up as "the weak exist solely to create things for the strong to take." You are worthy of having things if you are strong enough to take them, but only so long as you're strong enough to keep them.
The closest political ideology I could ascribe to him would be "stateless fascism." Andros is certainly sadistic, devoid of empathy and believes himself to be supreme, but he's too intellectually lazy to bother engaging in justifying why he's supreme. He makes the most basic of naturalistic arguments (i.e. "this is just the way the world works") but feels it's beneath him to actually justify or provide evidence for his claims.
He hates the minutiae of day-to-day life, and derives no joy from anything that doesn't involve someone else's discomfort or pain. He will steal your food for the sheer thrill of having taken something that you wanted to eat, but he won't enjoy eating it because he despises the physical sensations of chewing and swallowing.
And if you are a Hell Hound who, god forbid, enjoys something, he will bully the shit out of you. He will verbally and physically abuse you until you learn to hate the thing you liked just to make the pain stop.
Lemme tell you what the average night on Fort Cerberus looks like when you're not on a raid: you and a couple hundred other sick fucks lurk around the corridors drinking and gambling but you sure as hell better not actually look like you're having fun because you're all desperately trying to avoid becoming the bossman's next chew toy.
Some poor fuck catches Andros' eye. You're not sure what for, but from the sounds of things he might've been counting his poker winnings too loud. He gets a hand on his shoulder from the big man, who tells him that he's being too selfish - gotta learn to share a bit more, yeah? Now, way Andros sees it, guy's got ten fingernails that he's keeping all to himself, so here's a set of pliers - redistribute.
You jeer along with the rest of the room, loud enough to drown out his screams, because you're so very, very relieved that it isn't you. But you fuck up. You look a little bit too enthusiastic, perhaps, or maybe it's the opposite, maybe you weren't forcing it enough. Either way, the bossman's eyes land on you and your blood turns to ice in your veins.
"You," he says. "C'mere."
The room is dead silent all of a sudden, quiet enough that the pitiful whimpering of the first guy, (currently on his second thumbnail) is the only sound you can hear. You walk over, as a prisoner does to the place of execution.
He takes your hands, inspecting your fingernails, and then your hands, then your arms. "No ink yet? You not pulling your weight? Am I payin' to feed a fuckin' leech?"
You say you're not a leech.
"Those pricks over at the Gate are gettin' too clever. Learning too quick. Gettin' the jump on us too many times. I want someone over there learnin' what they know. You 'avin' no ink makes you a good choice. They'd sniff out any of these boys in a second, they would, but not you. You look soft. Don't he look soft, boys?"
The room jeers at you just as you jeered at the first guy (he's on his ninth nail, now, and his throat is so hoarse he can't make sounds anymore). You try your best to remain composed.
"Normally soft'd be fuckin' worthless. But soft'll let you blend right in with the Gaters."
So, to avoid whatever horrific torture he's currently ideating, you agree. The next time they go out on a raid, they pick a ship full of people who don't know each other and slip you in with the passengers when nobody's looking. You don't go to Hell's Gate directly - you do a couple of hops through the Thousand Habs, just to throw off suspicion.
You sue for residency on the station as a refugee from a failed habitat. They give you your own cabin, and they make sure you're fed and clothed. You smirk to yourself - they really are as soft as Andros said they'd be; they have food and water and clothes and they're just giving them away!
You don't have all that many marketable skills, so after a few rotations scrubbing air filters, you apply to take the militia aptitude test. You try to play it down so they don't get suspicious, but if nothing else you're a damn good pilot, so you get fast-tracked. These fucking idiots just give you a mech! God, it's gonna be so easy to tear them apart from the inside.
They put you in a team. You train together, building up hours in the simulators. Then something weird happens. They... trust you? They want to... spend time with you, outside the simulators. They want to drink with you, play games with you, hear about your life. Well, is it more suspicious if you say no? You have to maintain your cover.
You don't always fit in well. Sometimes you crack jokes that are... a little unpleasant, a little off, a little worrying, and you learn to bite those down because it's bad for your cover. You also have this odd air about you, like you're constantly on guard, like you're waiting for the other shoe to drop (like somebody's gonna make you rip your fingernails out if you're too happy). People figure you must've gone through some trauma and are kind stupid enough not to pry.
You feed information about the militia back to Andros - carefully, so as not to blow your cover. Some members of your team get hurt - nobody dies, but they get hurt. You feel... bad. Why do you feel bad? They're soft, they're weak, they don't mean anything. They're not your real friends. You don't have any friends.
Months pass. Jerry says he wants to tap your team for a long-standing project he's working on. This is your chance. Sabotaging this will prove to Andros that you're strong, that you're not weak, that you're not a leech, that you can pull your weight.
Sure, a bunch of your team will have to die. The only people who've ever put their trust in you, the only people who've ever believed in you. But that's fine, right? They don't mean anything, they're not real people, right? They're idiots for trusting you, right? They deserve it, right?