Although I would be wary of eating at any restaurant that makes most of their food with wheat four, if you find yourself at IHOP and are willing to take the risk, they do have an allergen list posted online.
As mentioned by others, they add pancake batter to most of their omelettes. (URRGH!) But they do have 'SIMPLE & FIT Spinach, Mushroom & Tomato Omelette' without batter. You can get that with fruit and/or Hash browns are also listed as gluten free. When ordering, I would make sure to ask the waitress to be sure this is prepared safely and they don't mix up your order.
Others mentioned that you *could* ask for any omelette without batter but I would personally be afraid someone would forget and poison me.
If in doubt, stick with coffee.