For GitHub and GitLab, they share the same ssh username git like g...@github.com:gitblit/gitblit.git
All the users share the same SSH username git. They differ the user by SSH keys.
For submodules, you have to specify the submodule urls.
Current ssh urls for GitBlit is ssh://username@ip:port/BuildFun.git
Then the username is different for every user.
And others won't able to grab the submodule because the username is different.
Now, I have to use relative path to solve this problem temporarily.
[submodule "SubModule"]
path = SubModule
url = ../SubModule.git