Could they be technically be executed like out of uniform Germans behind lines were in WW II?
It was well within the Geneva Convention guidelines then and would be a hoot to see what all these people whining about use of the Geneva Convention would say if we applied it now and strung up every single one of them.
As the Geneva Accords were written in WW2, yes. But I've heard it said that there have been several 'changes' made since that time. The biggest problem is that the Administration seems to be willing to let this "grey area" exist, and so they are open to criticism.
The Administration maintains that we have the right to try these enemy combatants in secret military tribunals. AFAIK, we have not done so. This suggests weakness on our part, and that translates to political weakness to politicians like Sen. Durbin.
If you really want to see these guys take sides -- flush the crazy leftists out into the open -- announce that the first group of detainees are being readied for trial.