I hope you are using low wattage bulbs. I would be concerned about it catching fire.
I just hope the government doesn't get involved in setting building codes for bee hives, or I'll be in trouble. :-D
Another option might be solar heated syrup. Maybe cover the top of the feeder box with polycarbonate; turning it into a mini greenhouse. That would probably warm the syrup up nicely on a sunny day. Sun provides something like 100 watts of energy per sq foot, that's more energy than the light bulbs.