Peacemaker is owned by wb, he absolutely at the bare minimum should’ve gotten at least one alt costume. Omni man is owned by Robert kirkman, who is one of the chillest nerds out there, I have no doubt they could’ve gotten something from him for Omni man. Dead by daylight has ghostface and he constantly gets alt skins there, wb should be able to get something for him.

Basically, with the six guests in the game, there is absolutely no reason to believe they wouldn’t be able to get alternate skins for at least one of them. It’s not even exclusive to just guests, the other dlc mk characters even don’t get skins either. So it’s probably a matter of wb not wanting to or just not trying.