Hi Jane,
I don“t think so. It's possible, but from mine understanding, the process of creating a users is far more complex than simply creating him in the command line. There are several tasks preformed by the system, such as creating the folders for the new user, setting the permissions, adding to groups, mail box configuration, remote access, etc.. So I sincerly advise you to keep working with server-manager. Is much more secure.
Regards,
Gabriel Requito