Either you know who he is or you don't, there is no barely.
This is a genius choice.
Jock is a secondary character, but a friend and compatriot of Indy. Because he is a secondary character, there are no detailed expectations, but there is a very clear persona communicated. The shirt, the banter with Indy, the snake, the plane: This guy is a wild adventurer that helps Indy from time to time. But because of the limited part he plays in the movies, that makes him a perfect character to expand upon. I am sure they had the idea and then searched for the character. Indy wouldn't have his own bar, he'd have a library. But Jock... You could see him turning a hanger in the middle of nowhere into a hangout for all his friends. A place where the crazy independent 1930's pilots hang out. And Indy might visit once in a while, or other characters. And who's to say he might not have a part in future movies? Although I doubt it.