From my entirely vague understanding of what Judaism might have to say about this, there's no religious problem, per se. If you want to baptise me in absentia, go knock yourself out. Just don't expect it to mean a damn thing to me or my family.

On the other hand, the act is still deeply offensive. These people died because of their religion and you've got the nerve to try to retroactively change their religion? When you're stomping like a bull in a china shop through somebody else's sacred history, the results can never be good. You might as well try to retroactively convert past Popes. I'm sure Catholics might take some exception with that.