Can Corruption be retargeted using droid Mark? It says it's only for living targets which a droid is not. Any help would be nice.

Based on the wording for the two abilities, here's the way I see it happening.

Darth Revan declares that he is going to replace his attack phase to use Force Corruption, and spends his 2 Force Points. At that time, if the piece that has been Droid Marked could be a legal target for Revan, then it may use Draw Fire (this is the tricky part, as the Droid has to be a LEGAL target for Revan, i.e. either no cover, or the closest enemy if it has cover). If Revan fails the Draw Fire save, then he loses the Force Points, and his Attack for that activation, as Corruption cannot be used on a Droid.

Might want to clarify it with NickName, but I'm pretty sure that's how it will work.

I believe the FP are spent, no matter what. Whether a character can be affected by an ability/power or not does not mean they can't be a target for it. If Revan fails the save, he targets 3PO, and nothing happens.