Aikido has a lot of merit as a self defense system. The emphasis on moving to a "safe" place, then executing one of the many useful techniques is wonderful.
A skill Aikidoka would likely fair well when confronted by an aggressor of a different tradition. In no small part, because the Aikidoka would likely seek to avoid violence all together, but still resolve the issue at hand.
However, what if there was a confrontation between two Aikidoka? What would happen?
Aikidoka practice is to throw and be thrown without causing or incurring harm.
I think that if the two Aikidoka's judgement were clouded by the passion or the moment, they would just have to work it out when they were to tired to carry on the fight.