I have been looking at various git clients to see if any of them will work with Hook. I was unsuccessful to find anything that would let me link to individual commits. The closest I have come to something to keep an eye on is Tower. They do have one URL scheme (not powerful enough to date), which tempted me to contact support. Here is what I got back:
At the moment the URL scheme is indeed limited to opening repositories.However, providing deep linking to individual commits and scripting support is quite high on our priority list. I’m unable to give you an ETA as of now, but this is something that will very likely come in a future version of Tower.
I thought that answer was promising enough to pass it along.