Eggcrate should be fine under the lights, I have been doing it for a couple years. Cats(most) don't like to walk on grated surfaces like that so they shouldn't try.
PS -- My cat did go fishing before the egg crate, as he was just jumping onto the tank he realized it was open and tired to make a mid air turn but still ended up half wet. It was a good way to test my new skimmer by seeing it pull cat hair out of the tank.