I didn't realize that you had replied until now.. Sorry - I'm new to gitter.
There are one limitation in the tree visualization algorithm if it's used for git -- it does not handle branch merge, which happens in git a lot but never happen in vim undo history.
Ah, that makes sense. Too bad.
Except that, I think "git log --graph" or "gitk" would be enough in most situations.
I assume here that you mean that running these commands should be a good alternative to having an undotree-like plugin. I disagree though, I think the ability to scroll through file history from within vim, using j/k/enter to show revisions in the current buffer is much more powerful than copying/pasting git refs all over the place.