awkward question

No, you can't make a giveaway for a desura key. HOWEVER you can activate the game on desaura and retrieve the steam key and make a giveaway for that.

I think it's a tricky one. You hold full responsibility of the giveaway in that case. As long as the winner activates the game on Steam, all should be fine. But if something screws up, it's your own fault and support won't help you at this point.

It gives a Steam key, so I don't see any problem with giving it away, You could also make another Desura account, activate the game and give away the Steam key :p

Can't you give the desura key to a "real life" friend and then make a giveaway with the steam key? So you don't end up with 2 Desura accounts with the same game.

If you don't wish to make another desura account, look for somebody with a solid reputation on your friend list and ask them for help. What game is it, btw? Would it be hard to replace, if something went wrong?