We must avoid theater becoming a superspreader event. I don't know the set up of this particular show but an indoor theatrical event in a small poorly ventilated space and actors unmasked talking or worse, singing (see: Skagit Choir) checks all the boxes of a potential superspreader event, even with most of the audience vaccinated and/or masked. If the actors cannot be outdoors or masked, they must be vaccinated. (That should also mean the production pays them at the same rate as their other work for the time it takes to get vaccinated and recover from any side effects.) It's not that hard.
Separately, I'd encourage the original poster to read some of the latest data on Delta and the vaccinated. The original scariant headlines that Delta was "equally contagious" among the vaxxed and unvaxxed don't pan out on further inspection. For one, the infectious period among vaccinated breakthrough Delta cases seems substantially briefer than unvaccinated-- but such hasty reporting and confusing messaging from the CDC has contributed to the fact that over 50% of unvaccinated people give "the vaccines won't work as well against the variants" as one reason they have gotten the shot yet.