It is an important part of the administrator role to be present at all forms of extra-curricular activities; thus, they should attend your plays just as they attend sports events, debates, concerts, etc. Seeing your students perform in a show you have produced is part of demonstrating what students have learned in your classroom. I would, however, be wary of only having an administrator see the final product of your (and your students') work. For a teacher evaluation, the administrator should see the full range of what you do with students- your in-class interactions, how you adapt your teaching to the individual student needs as they arise, the structure and organization of a theatre lesson (which is often very different from what is seen in a 'core' subject class), etc. Absolutely invite administrators to your shows... but make sure they see what you do with your students on a daily basis in the classroom. The process is necessary for an evaluation of your teaching practice.