Currently a manager can create new collections and share them with all groups which exists in the org. But he can´t see which group have which members.
Also he can´t add new people to a group.
An admin could do this but an admin could also give himself more rights to see the hole (organisation)vault.
I would prefer that a manager could add people to his group(s) like he could add new collections and of course see the members of his group.