Does it matter? "Regular" people won't pick up on the reference to git, but it's still a nice short domain name, easy to spell and pronounce, and git is a slang spelling for get. I think the name works well.
I think you're right. It's a good domain name and "regular" people won't pick up on the reference and won't really care regardless.
In my book, not exactly. It's more like the mildest possible term of abuse. You could generally get away with calling someone a git to their face and in front of their grandmother. Assuming they'd done something tricksy or cheeky or grumpy.