Is it OP as support nunu and their ad carry to get a perma blood boil? Seems like their ad carry has an extra passive skill.

Nunu, I feel, is an incredibly strong support. He can zone with his e, has great sustain on his q and then w. His blood boil is working as it should be. It if not a broken mechanic and it is one of the only things that makes support nunu viable in the first place. I, wouldn't call it op

Lets take a look at the weaknesses of a nunu support:
Lacks hard cc, you can pick a few champions that are cc machines (Alistar, Cho'gath, Naut) to pick up the slack.
Lacks a heal or a shield for teammates. Further, the downside of him relying on comsume to keep up his health is that he is stealing cs from the carry. That is only okay when there is no friendlies in the area. Aside from that, you do not steal cs.
His ultimate is hard to land. It takes good positioning, a spell shield, a very distracted enemy team or an enemy team lacking any cc that can stop a channel.

His strengths:
His passive lets him cast spells for free
His q is a very nice anti-dps tool
His blood boil helps increasing the dps of friendlies.

nunu doesnt have a heal, so it forces them to be both highly aggressive and careful at the same time, it seems OP but you should see the graves/sokara combo...

I like nunu support solely becuase I can take cs with Q and say its a nessisary lose (of course i do it if i'm missing >30% health)

lol support nunu haters. support nu scales into late game because adc is becomes god/goddess mode. soraka is.. soraka. as useless as she can be once laning phase is over. unless she's ahead or a super poke comp! but really. why alwasy compare nunu with soraka? they have nothing alike aside from offensive and defensive buffs.

what about tarics auras? plus you cant just spam blood boil or you wont be able to use your other abilities because of the mana costs.