...She doesn't look like any kind of demon he's ever seen...but he can't immediately think what else she could be. (He's unconsciously assigned her a gender based on her voice.) Certainly he would be more surprised to find something that looked like that fighting for the crusaders than for his own side.
Of course, "his own side" is relative; he's seen plenty of skirmishes between Baphomet cultists and Deskari cultists, in his line of work, and even when everyone serves the same demon lord, that doesn't make them all one big happy Evil family; the number of minions he's seen Hosilla casually murder for annoying her has been...educational.
So the question is, really, what risks he's running and what benefits, by cooperating with and/or pissing off this giant starfish creature.
If he pisses her off, the obvious consequence is that she murders him. He doesn't know for a fact that she can do that; it wouldn't be maximally wise to assume she can't, given that she is a giant unidentified talking starfish monster, but on the other hand if you never take risks you never get stronger. Back on the first hand, it can be smarter to take on risks you have a better chance of evaluating.
If he cooperates with her, the worst-case scenario is that Baphomet personally gets pissed off about it and tortures his soul in the Abyss for a long time. More probable and immediate potential consequences involve Hosilla or her Hand personally murdering him and making whether Baphomet notices him to torture or not immediately relevant. On the other hand, while he does know that either of the Hands of Hosilla is definitely stronger than him, that's more the kind of known risk that it makes sense to take in pursuit of strength, and also even if the starfish critter isn't relevantly on their side, if she's really strong she could eat the Hand of Hosilla instead of him, or if she's not really strong the Hand of Hosilla could look favorably on him for giving him a weird thing to murder and exaggerate about.
Well. That's that decided.
"Wait here. I'll go get him."