RE: LA Modern Noir: Chapter 5c Allison

Is he overly a caricature?

He does have that feel. The trope of a guy whose greed has gotten the better of him and wants to make as much money or name in the gang as fast as he can.
He seems like that kind of character whose insecurities have gotten the better of him and that the boss (Harry) would drop in a heartbeat when he's no longer useful.

I wonder how Alisson would fit in such a scenario if it does happen.

And did I get the balance of revealing horrible action without it being gratuitous or titillating

Yep, you got that well. At first I thought why was he doing this, like what's the need?
Then I realized that's him as a character, a man of violence and Alisson is the punching bag, as Harry said, he's a creature of habit, and as the neighbor who visited Allison in the next chapter further revealed, he always beats her badly before he went out on a multi day trip.
Hence the rouse of her dressing up for assumed sex was just a rouse, we as readers don't even know if they did eventually have sex, it was just a total gory beat down