I've read differing opinions regarding adding WC isopods, as well as mixing different species.
The most cautious people will tell you to breed the wild caught isopods for a generation or two in their own tub, removing babies to their own bin to limit exposure to any parasites that the WC parents may have. Others will dump WC isopods into established enclosures. I fall somewhere in the middle, and while my WC isopods have their own master cultures, I havent been separating the young.
When you house more than 1 species together, there's a very real chance that one will eventually outcompete the other. They won't necessarily eat each other, but they will potentially starve each other out/horde resources! If you give them enough food and good places to hide, I dont think it'd be as much of an issue. I have (accidentally) introduced sowbugs to my o. Asellus culture, and they've been coexisting for about 4 months without any discernable problems. The o. Asellus have hides that they cluster together under, and the sowbugs have their own favorite spot.