I vaguely recall that the original P4U story established that the main villain was someone who didn't have a Persona and therefore couldn't enter the TV world, so he had to get someone else who did have a Persona to go inside for him. So now that we see these two Sho's, one with a Persona and one without, you can sort of assume that they are different people, and maybe by extension two separate characters?
Also, for the people wondering how Adachi is going to deviate from Naoto's playstyle, I'm gonna guess dual-wielding pistol and police baton lol... Actually that sounds really badass...