They definitely are. I don't quite known what your 'Persona' is -

[He'd require more study and he's relatively certain that an offer of such is not going to go over well.]

- but demons do have quite a lot of agency. They can't harm their pact partners, but they can do all sorts of things within the confines of a pact. The ones I designed are relatively strict, where the demon can't do anything physically or mentally to harm their summoners.

[Emotionally is free game though.]