Even if you can only shoot at the final dress rehersal, and from off-stage, Nicole, I think I'd try to talk to stage manager to see if you could get access to the stage, with the lights on, to do test incident metering prior to the start of the dress-rehersal performance (relating to my diagram suggestion). Also, ask if there are significant lighting changes that will occur during the performance.

I'd think if you convey the idea that you want to stay out of their way, but want to capture the full glory of their efforts, they'd be likely to cooperate. They may start with the attitude that the photography is a nuisance they are forced to put up with, but a little ego stroking might go a long way.