Mine investigates anything new in the tank...and I mean ANYTHING. He considers anything that comes from my hand to be food till proven otherwise. I have four shrimp (two blood, two cleaners) 3 or 4 pistol shrimp (two that I put in a couple other hitch hikers) and he hasn't threatened them at all.
I used to think he was killing my snails but when I found and removed two large polyclad worms the snail deaths stopped for the most part.
I bet you will be fine adding it at night.