If you have the commit hash of the commit(s) introducing the bug, the it's a simple matter of seeing if that commit is an ancestor of any commit (or branch) you're interested in. Similarly, once fixed, it's just a matter of seeing if the fix is an ancestor of the interested branch/tag/commit. (Not saying that this tool couldn't or shouldn't, just simply that this should be very doable within git, I think.)
I imagine the most difficult part of this is just getting the data collected. Even with git-bisect, I very rarely find myself looking for the point of introduction, and instead just fixing the bug.