Yes...Mali's can be housed together, but nothing is guaranteed as to how they will get along. It is not necessary to have them together (as far as they don't get lonely being alone and are quite happy having the run of the place to themselves) but it can be done.
One thing that was specified to me to make it work the smoothest, was first, to have opposite sexes. You really shouldn't house same sex for it mostly likely will never work. Next is to have one much larger than the other. I guess they don't tend to compete as much when one is more the "dominant" one.
so far I have housed 2 different pairs together and it has worked just fine. Also make sure you have plenty of hiding spots so that they are not forced to share one. Also may need seperate food dishes as well. And most importantly, make sure you have the $$$ and room if for some reason they do not get along and have to be housed seperately. Can be quite a chunk of change having to double up on lights, etc.
Other than that, good luck! 
Renee