Will adding beet pulp to my horse's diet make him hot? Need some extra calories.

No, it is pretty amazing

No, not unless your horse is somehow allergic to it. There is little sugar in beet pulp. It is the remaining bulk after all the sugar is pressed out of the beet. My horses have been on beet pulp for over a decade, probably closer to 15 years now and I can't imagine I'll stop using it ever. 

I do feed beet pulp. I was just reading an article about the benefits, plus a lot of feeds contain beet pulp already. Mine are not hot.