There's always a chance that he will and there's always a chance he won't. I've had my 2 ft alligator gar in his home with a school of about 50 neon tetras, he didn't mess with a single one.
I've learned over the years that if the gar is big and his tank mates are "smaller" then he wasn't even going to waste his time eating them.
I've always had a "routine" feeding with my gars so they knew "Dad is gonna feed me fresh shrimp and smelt, why do I need to eat these minnows"... Type of thing.