Last night it took us at least twenty minutes to get out of the theater parking lot, I wished I was on my bike

What a great idea! Go for it!

On the cautious side: Though you provide surveillance, you should still inform customers that they are parking at their own risk, decline responsibility for any damage, theft, etc, just because you do not have the facilities to accomodate a secure enough environment for bike parking. Decline responsibility for accidents occuring on theatre/lot property. Warn of hazards of riding at night, use lights..

If you decide and once you do it, let us know how successful it was!