I actually was finally able to track down the cause of being unable to res some corpses. In spells.cpp around line 2250, the part of the if-statement that says
Code:
!IsBeneficialAllowed(spelltar) ||
actually varies for the corpses. Sometimes this call returns a 0, and the corpse is deemed ressable, other times it is not. I haven't determined why this occurs, but commenting that condition of the if-statement out has resolved the problem on my server.
As far as the player being in the same zone, I had this issue creep up when the player was in the same zone, and when they are not, so I don't believe its related to that in any way.