Hi @Lance_Levin,
Sorry about this, it's a case that I forgot about as we addressed it in our instance a while ago. Because users all actually exist at the root account level, the user needs to have a role with the "Users - manage login details" permission enabled at the root account level. We created a role called "global privileges" and gave it this permission, then added our subaccount admins as admins in the root account with this limited role as well. It does make all courses available to them in a very limited view, but will then let them add users on their subaccount page (or the root account one, since it's really all the same in the end).
Again, apologies that I forgot about this particular limitation originally.
-Chris