Of course you can, the question is should you do so? and I like others don't believe in mixing species. I don't own hermanns, so I can't comment on their care, but it is a bad idea mixing species even those that have similar care. I don't see a problem getting them from different dealers.
I agree with Dmmj. Even if they have the similar care, they carry different bacterias, some that does not hurt one specie but could make the other sick.
Different tortoises from different geographic locations should never be mixed. Each tortoise may carry pathogens and bacteria that the other has little resistance to. Don't mix species.
I love (not really) this, because there's a shop in the area that houses a russian, a sulcata, and a redfoot all together. Their housing requirements are not the same! I can't visit that shop because every time I go in there I want to cry.