It's been many moons ago but .... tried to help a FC School use FC for authetication. Never could get it to work.
In the form for setting up FC, http://yoursite//admin/auth_config.php?auth=fc it does say:
Userid for FirstClass account with privilege 'Subadministrator' set.
So I'd say yes.
FC should be like LDAP in this case I would think and am sure your FC Server Admin person might not like Moodle (if it could) creating new users. BTW, it can't. That sort of thing could lead to all sorts of troubles for the functioning of FC, would think.
Supposedly (remember, couldn't get it to work), the closest to 'creation' is:
The config fox for Password change URL whose help says:
Here you can specify a location at which your users can recover or
change their username/password if they've forgotten it. This will be
provided to users as a button on the login page and their user page. If
you leave this blank the button will not be printed.
Might want to check into FC official docs and resources. One of which is:
http://sync.firstclass.com/__Help/FOV13-002F1E57/FAV13-002F1E49/FOV13-002F1E4A/S06703C57-06703C5E?Templates=Help
Good luck!
'spirit of sharing', Ken