As a rule of thumb, you dont mix pets. Based on that info I woudnt mix anything if i were you, but someone else here might have had some success with mixing. If no one else has, i wouldnt try it unless you are willing to lose the pets. But hey, maybe they will be fine (as long as there is enough room).
There have been may hobbyists who've been successful keeping other species of Pandinus with emps (P. imperator), and even Asian forest scorpions (Heterometrus sp.) as well. If all are adults and close to the same size, you may not have any problems. Then again, you might, there are no hard and fast rules. If you try it, kep them well fed.
Well, I don't know about emps (never tried with them, but will tell you how it goes when I try), but I keep a lizard native to the area I'm in, with almost all my desert and scrubland scorps (Hadogenes try to eat them even though they are cool lizards, so they don't work well at all). The other scorps share burrow (scorp protecting and killing food and liz keeping the place clean, I suppose *lol*)
Well, my assumations of the reason it wont work with a rainforest is because the humidity is already quite high and I believe the desert scorps enjoy the extra little bit of humidity they can get from the liz, as well as they eat any left over food the scorpion has.