ajiziboc,
Unfortunately there isn't a report that I am aware of that will show that to you. You will have to go through everything in the system that can have Extension Lists in it and verify that; not only Hunt Groups use Extension Lists.
So, CO Trunk Groups, DID Routing Tables, Voice Processor Applications, System Forwarding Paths, Associated Extension on a phone can all go to an Extension List unfortunately.
Sorry,
TE