From what I've read, the mechanics of hitting are very much alike in softball and baseball. One person who has coached both major league hitters and pro softball hitters states that 99% of the mechanics are the same.
Regardless, if a person watches batters closely and often enough, studies all the video tape available, and gets trained/mentored by other baseball hitting coaches, that person can most definitely learn how to be a great hitting coach.
Yes, it might be a hard sell to baseball players to be coached by someone who hasn't played baseball. But that is because of their own biases, not because of anything factual in their beliefs.