Instead of trying to automatically format the project when someone does a commit, I would run cargo fmt --all --check in the pre-commit hook to check whether the workspace has been formatted. Then, if the workspace isn't formatted it'll abort the commit and force the user to run cargo fmt manually. I prefer that sort of manual intervention over automagically formatting the code before each commit.
In practice, having a commit aborted due to unformatted code isn't a big issue because most IDEs will format on save.