I have had many ESP/LTD guitars with EMG HZ's...They used to be in all the 300 series LTD instruments. WItht he 400 series came active EMG loaded guitars.
The H4 is the passive 81, the H1 was more common in the early days of the 300 series. I think they have a little lower output than the H4, but I think they sound better. The H3's and H4's have a solid cover on them, while the H1 and H2's have one row of exposed pole pieces. I can't remember any guitars that came loaded with the H2's or H3's, though, it's usually H1's and H4's. Also, each model has a variant of the pickup that uses alnico magnets over their ceramic counterparts (designated as H1A's, H4A's, etc.).
I'm with the others who think EMG's strong point is active pickups.