Whether Bruce was the greatest Martial Artist or not is debatable, but he was a true Martial Arts genius.
I remember reading about Aikido somewhere in his Tao of Jeet Kune Do or some other of his books that I possess.
He was always open to ideas and the underlying philosophy of Jeet Kune Do was to liberate yourself from fixed styles and absorb what is useful from every Martial Art and Philosophy. So, if he had had an exposure to Aikido, I don't have any doubt that he would have incorporated it in his system.
As for using techniques against him, I don't think I would ever be able to do so. However, visualizing an attacker as fast as him, I can think of only irimi nage as something I'll be comfortable with.However, on my good day, kotegaeshi
might just work, as it happens to be my favourite and seems to work effectively against punches.
But, why fight him? There are lot of things to learn from him and that would be the right attitude when facing Bruce Lee.