That's not been my experience (in a previous life I did 5-6 shows a year, and was yelled at by union reps more than once for hand-carrying my own materials in). At the shows I did (which included venues like the Cobo Center, various downtown hotels, and other union-heavy shops), the union electrician would wire up an outlet for you, but you were then free to plug in what you wanted (as long as it was UL-listed).