It's easy enough to start with an uncooked chicken, or better yet, wings for the high collagen content. When you start with a rotisserie chicken, you've a lost a lot of the chicken's flavor to the roaster's drip pan.
I prefer the flavor from the already-roasted chicken in my stock, but yeah a raw chicken works just as well. Just needs more cooking time in the pressure cooker. My main point was that making stock at home is a lot faster if you have a pressure cooker.