Re: Aikido does not work at all in a fight.
I think a practitioner of any particular art or style, if entering a "NHB" event, would fair better if they simply fight without trying to use specific techniques from their art.
They can use what they've learned, but it isn't likely that their opponent will cooperate by replicating scenarios that they've trained for back in their home dojo.
That said, a practitioner of Aikido will probably have to adapt more than people trained in some other arts (i.e. Thai boxing).
A few months ago, a black belt in...I think... Kenpo visited our dojo for practice. Following the practice, this guest was invited to show us all some of the techniques from his style.
One of the members of our dojo (a 5th kyu at the time - and someone who, incidentally isn't very gifted or coordinated) acted as uke. Coming from a more..."confrontational" style than Aikido, the guest started to get a little rough and our uke resisted back.
They sort of got into a friendly competition and our 5th kyu basically was able to control the Kenpo black belt. Granted, this wasn't all out fighting with strikes to the face, etc, but I was pleasantly surprised at how well the Aikido techniques worked in the face of resistence, from someone with presumably much more training in a different art.