they get the bebuff, but it doesn't stack so no dmg boost for the non raid melee characters. their DPS is just the average normal DPS. that's not a buf, the raid has to stay focus on its task.. dps as much as possible
And I Get there with the down of patcwerk (easy as hell) and grobulus, also easy (just friend up with a healer in your guild) and when the poisoning bomb pop on one of your shamies... go blow somewhere close to the walls (with all your shammies, pop the nature resist totem and cast the healing wave on eachother : easy easy easy .

I've been through Naxx 25 with at leat 3 of my 4 shamies and managed do down KT as well (ss below)
http://dual-boxing.fr/forum/showthre...13480#pid13480

the only Boss I can't kill (with shamies alive) is Heigan and its stupid freaking dance !!