If you're going with LEDs, I'd suggest some sort of guard, not even so much for moisture as for grease spray: imagine what's going through the air when you toast up your morning strips of bacon!
Undesirable effects of grease spray probably include, softening, yellowing, swelling and crazing of various plastics (e.g., LED lens, or those jelly things the strips are made of), plus difficulty cleaning up (it gets sticky after a little while).
The LEDs recessed behind a semi-sacrificial lens or plate would be good. Glass sealed with an O-ring would never wear out and would be easy to clean, but you don't need to go so overboard just for this; a polycarbonate or acrylic plate will probably do as well.
As long as the back side is well ventilated, what's going on below doesn't matter. You'll want to make sure there's some circulation behind, where the LEDs are. This could be passive in the structure, or active (hey, you could tap some suction from the vent fan, so it draws clean air over the electronics, from somewhere else; or draws interior air still, but through an air filter).
Tim