Managers can add both member or non-member teachers.
To add teachers to the system, click "Users / Teachers" in the manager menu, and then click "Manage teachers". That will show a table with all the teachers in the system. Once there click the link on top of the table: "+ Create teacher".
The teacher creation form will give you the option of making this teacher a member or a non-member by clicking the checkbox.
In "Teacher code" you may enter the MTNA ID of the teacher, OR leave it blank for the system to generate an automatic code.