As far as I know, Komodos are the only monitors that have been proven to have any real venom. Monitors (wild ones at least, don't ask me about captive) have infectious saliva due to their rather unclean diets. So rather than a venom attacking the nervous system or cardiovascular, it just gets really infected.

Tegus and monitors do have an anticoagulant in their saliva, and that I can say from first hand (literally, my own hand) experience. A 3 foot tegu bit me and it bled for 3 days straight, non stop.