Shared write access to the same git repo directory can be done sanely, but you have to get a number of things right (same group for all users, everything group writable, sticky bit on directories, set config core.sharedRepository=group): https://stackoverflow.com/a/29646155
Yes, when you're not on NFS. Maybe it works on NFS but I wouldn't bet my project on it. Locking reliably on NFS is easy to get wrong, and it's a comparatively little-tested scenario now compared to 30 years ago. (You'll notice that the question doesn't even mention the possibility of NFS.) Fortunately at least with Git it's easy to have lots of backups.
That makes me a little less suspicious, and of course the Git developers are well aware of things like concurrency problems and filesystem limitations. But I'd still regard it as an area to be wary of. But only if two clients might be writing to the same repo concurrently.
