The only way I've beaten this combo is to blow up the lock ASAP. You can live through the silences/polys/etc., but the spell locks and devouring of the felhunter, and a GOOD lock in this combo will be spamming Curse of Long Ass Casting on your group constantly, he has to go first. The biggest killer in this group, imho, is curse of long ass casting on your healer - since only druid healers can remove curse, priests and paladins are highly vulnerable. Add in the silences, and mass dispels from the spriest to remove your bloodlusts and their damage will come faster than you can heal.

The 2nd place team on my bg was running this comp, now their shaman has respeced elemental (31/9/21) imp grounding/instant ghost wolf for escape, they've replaced the rogue with a holy paladin. Pure caster team, with the ns/em combo + shatter crits. IMHO, this is by far one of the best 4 dps teams out there with earth shock/counterspell/silence/spell lock at their disposal. Curse of Elements makes all the damage you take even more powerful as well. So they curse of elements one person, instant cast dots, heroism + nukes, plus a lockdown and cc on everything but their FF target and it's gg fast.

Edit: Oh, and against this team, I don't purge at the start and my priest knows not to dispel. I wait for a grounding to drop so I can purge it away instantly so my LB volleys don't go into the ground - which gives me about 10 seconds of damage before another ground will come down.