Proteinase K is active under a wide range of conditions, so it will probably work. The question is, how are you going to inactivate it so that it doesn't chew your restriction enzyme?

Thanks! I also started from the assumption that it is very robust and tolerant to conditions, so it could work. I tried it but the final result of my PCR is not convincing so I try to break the possible problems apart and thought somebody might tested.

Inactivation is exactly the next problem :) I did a 15' incubation at 98C, as a guess. I know it is almost impossible to completely inactivate by heat, but that generally takes away enough activity.