Hello, HMHorseluver, and welcome to Zoo Admin! It's always wonderful to see new members here! First of all, why don't you go and introduce yourself officially on the official
introduction thread! I'm sure there's many people just waiting to welcome you!
As an answer to your question, not all ZT2 downloads need the ES to function properly. The downloads should work fine unless it is specified by the maker that they need the ES to work properly. All downloads will specify if they need the ES or not.