It's not about religion when we're not mixing lakes, there's good reasons for that:
Mbunas are way more active fish than the finicky Tropheus. They will continuously outrun them for food and space.
Tropheus and Mbuna diet might be similar, but the feeding behaviour is absolutely different, excepting a few of the Mbunas (Labeotropheus species, Tropheops) that might have similar feeding patterns. The dentition of a Tropheus helps them maximize the amount of algae they rake from the rocks and excepting a couple troublemaking males, they usually hang out together and don't spend a lot of time moving around. The Tropheus pretty much try grazing all the time quietly while the Mbunas are very adapt to pursue open water nutrients and their mouths help them in doing so as well, as their frontal facing mouth have dentition that help them maximize the amount of nutrients they can catch in the open water column and they are fast, very fast ...would you agree with me? Not to mention the nipping abilities of an Mbuna's mouth are very well recognized.
For me, mixing different biotope species is not the best idea. At the moment I only have one tank left, but saying that you mix varients from different sides of the lake is not the same with mixing with fish from different lakes. I am not going into water chemistry (which is normally only relevant if you're keeping wild caught stock) ...bottom line is, Tropheus should be the dominant fish into one's setup and could be mixed with other, smaller fish that cannot damage them, or stress them. Tropheus bloat is very well known to wipe out entire colonies and the active Mbunas would just add to the inter-specie stress and increase the risks of one's colony getting sick.
Again, I wouldn't mix the Tropheus with other more active, or more dominant fish.