We went there for the first time in February - yes, they are on the
DDP for sure, No, they don't take ADRs (but they are considered table service).
If you walk through the doors to Teppanyaki, the door to Tempura Kiku is straight ahead next to the hostess's station for Teppanyaki. We went there one evening about 5:30 and when we got there, only a few other people were in there.
I think that people are SO over-eager to eat at Teppanyaki. We have eaten at a lot of hibachi places and so it's nothing special.
The service we received at Tempura Kiku was EXCELLENT. All of the waitresses had not been in the states very long at all and were still sort or getting oriented. But their English was great and they interacted w/ our 3.5 year old DD so well. DH was born in Japan, and so it was a great cultural experience for us and we'll look forward to returning to this restaurant next year!
The previous poster is correct, the seating is pretty cramped. It's very much like sitting at a u-shaped sushi bar - probably no more than 15-20 seats total. The cooking takes place in the middle, so you can watch them - I was really surprised that all the grease didn't overwhelm us but they must have great ventilation.
I definitely would recommend it, especially if you have gone to a teppanyaki place before - I keep hearing the one at WDW is really nothing superior over any others. Also, the counter service Japanese place is great too - Yakitori House.