I see it done all the time in
pet shops, but personally I don't think its a very good idea over the long term. The problem being that they will tend to compete for the best basking spot, and inevitably one will be dominant and the other will be secondary... it may not affect them directly in a physical sense, but it is a psychological thing as well. And in the long term, possibly not enough heat, light, and psychological well being can't be good any way you look at it. I don't see why they couldn't have a communal area for 'play time' though. As long as they are friendly to each other... but I really wouldn't keep them together in the same cage all the time.
*shrug* Its hard to really say though, I'm sure it could be done and it would work... but as a general rule, housing different species together is not recommended.
You have any pics of your mali?
Rav