I found the answer after searching some other posts - it's in the combat section of the PRD:
Supernatural Abilities (Su): Using a supernatural ability is usually a standard action (unless defined otherwise by the ability's description). Its use cannot be disrupted, does not require concentration, and does not provoke attacks of opportunity.
and for rage:
While in rage, a barbarian cannot use any Charisma-, Dexterity-, or Intelligence-based skills (except Acrobatics, Fly, Intimidate, and Ride) or any ability that requires patience or concentration.
So the supernatural ability doesn't require concentration and it's not a skill. As long as the GM rules that it doesn't require patience (can't see that this one would) - I should be good to go.