Its never a good idea to just have 2 Tropheus. They prefer much larger groups, as in
mbuna like stocking, 12-20 fish depending on tank size. Other then that though, i've heard of it being possible yes to keep two types of Tropheus in a single tank, assuming they are not of the same species because they can and probably will interbreed if given the chance. Recommended? Ehhh, a purist and someone else will fight back and forth about it. Who knows. As long as they arn't overly aggressive to each other or anything else, are healthy, and are eating (because they eat the same thing so feeding isn't a problem) then why not? They really can be bullies though so just keep an eye out.
If it were me doing it, i'd have a larger group to spread the aggression out some. I'd treat them much like an aggressive type of Mbuna from Malawi as far as tank, groups, and feeding are concerned.
To answer your question bluntly, yes it is possible to mix two different species of Tropheus together in a single tank.
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