I don't mind an ump pulling a coach aside after a game, or before and giving them the wisdom of his/her experience.
A lot of people might feel that way...as long as they are on the receiving end of the beneficial advice.
What if the umpire is giving his "helpful tips" to your opponent and they use that information to gain a competetive advantage over your team? Maybe you're cool with that, but it's easy to imagine that some people might not be.
If you want to be a coach, then sign up to coach a team. If you want to be an umpire, then you should keep the coaching to yourself. One of the umpire's goals is to remain totally impartial and unbiased. He should avoid anything that even hints at helping one team gain an advantage over another.