I'd vote for the ghost shrimp as well. I've never seen any of my 3 bolivians nip a fin, even on each other. They are all talk, they never do any damage.
Endlers are related to guppies and are very peaceful..I have a hard time believing they'd nip a guppy.
Ghost shrimp I've never owned(I have cherries), but shrimp are weird and opportunistic. I wouldn't put anything past them.
