Is it convenient to use git-vendor to collaborate with people who don't have it installed? Or everyone working with this repo must install git-vendor, even it he doesn't going to add/update/remove vendored dependencies?
You need git-vendor only for vendor management. All stuff is actually just normal git commits, so if you don't want to add/remove/update vendored stuff, you can use git without git-vendor as usual. Without git-vendor it's like a normal git subtree.
How to vendor a git into another git