Does everyone bruise when their joint dislocates?

Not always: It is possible to dislocate without bruising, but usually a dislocation is accompanied by joint swelling and bruising by about the first few hours. It depends on how traumatic the dislocation was on the surrounding tissue. Be sure to get the joint evaluated by a physician if your suspecting a dislocation.

Yes: To dislocate a joint you have to tear ligaments and soft tissues, the tearing implies bleeding and the bleeding is what creates bruising to at least some degree.