Appears so in 188.8.131.52 here. From git-submodule(1):
Flag to `add`:
> -b, --branch
> Branch of repository to add as submodule. The name of the branch is recorded as submodule.<path>.branch in .gitmodules for update --remote.
Flag to `update`:
> This option is only valid for the update command. Instead of using the superproject’s recorded SHA-1 to update the submodule, use the status of the submodule’s remote tracking branch. The remote used is branch’s remote (branch.<name>.remote), defaulting to origin. The remote branch used defaults to master, but the branch name may be overridden by setting the submodule.<name>.branch option in either .gitmodules or .git/config (with .git/config taking precedence).