So the paradox plays out, and we are back in the present, where Rory is again zapped back into the past, can the Angels feed on his life energy twice? Rory would not have had any energy to feed off, or was the first time paradoxed out of time, despite us seeing the grave at the start of the episode.
It's probably the same gravestone, but different circumstances of death. Think Back to the Future III where also just the inscription changed.
I also wondered if Angels can feed of a person twice and and thought that was the reason Rory was just displaced in space and not in time when the babies got him but apparently that is not the case.
That said, he is a time traveler AND "lived" out 2000 years before. He is probably juiced up with enoough time energy to give River and teh Doctor a run for their money.... well, maybe not the Doctor.