I have done two H&H on an enduro bike where there was a chap on a Sherco trials bike (with no seat) who did more laps than me and plenty of others. One of these events had a fairly technical wood (for a H&H) - where a trials bike was possibly an advantage. Most of the lap time was spent in the wood. The other event was very open, mostly blatting across flat fields.
Unlike me, he was obviously a very good rider (and pretty fit I'd imagine!) but it just goes to show what's possible - although you would need to be careful with big bumps at higher speeds.