Is a portable air oxygen machine allowed into theatre, weighs about 8 Lbs.

As a Detroit firefighter i don't see there being any reason why it would be a problem. Feel free to go and enjoy yourself.

Yes they are allowed, I used to escort senior groups to the theater. I always had at least 2 people in our group that carried oxygen.

I haven't seen anything about them being prohibited and they aren't on the official list.