If by together you mean in the same tank, sure, won't be a problem... however, if you mean together as in "so close that they'll be touching", then one colony may burn the other, as they're different animals.
Actually, I'd think that they'd be fine. Separate heads of the same colony don't burn eachother. And I've put two different green slimers together and they get along fine.
I haven't tried it personally, it may not be an issue at all... but keep in mind that 2 heads in the same colony are the same animal (they'll retract together when one of them is disturbed) so it's normal that they won't burn one another, while 2 colonies will be 2 different animals that may have different reactions to attack and/or different levels of "chemical powers"... that was the only base for my reasoning.
Well they will be from 2 diffrent colonies.In regards to them being the same colony,when you frag a torch head off of the colony then it's not part of the colony so they would sting eachother.I don't think that happens but that's why i asked the question(not sure)