Yes, ZEP is a Scrabble word!

Letter values in Scrabble US: Z 10, E 1, P 3.

Is it a valid word?

ZEP is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

a large sandwich made of a long crusty roll split lengthwise and filled with meats and cheese (and tomato and onion and lettuce and condiments); different names are used in different sections of the United States

Also: hero sandwich, cuban sandwich, italian sandwich, poor boy, submarine sandwich.