from what i have read it is not a true 4x course and it has a moderately sized huck to decent tranny in it. it could probably be done with a hardtail but i would stick with a dh bike or some f/s mountaincross bike.
Its definately doable on a hardtail, one of my friends rode it on his Azonic DS-1 w/ 3" DJ3. He would also race downhill on that bike. Pretty much everything is "doable" on a hardtail, but in this case I would advise against it. A short travel mtx bike would be best. I wasn't there for the 4x race they had (if it even happened), but I really doubt they included the big jump and just did the go around. I did the DH race where the lower part of the 4x course was included and the jump isn't that big a deal but I wouldn't want a guy next to me as I went off it.
damn, I can only keep one frame, I have a Giant AC1 and an Azonic DS1. I think a giant is good for p-kill but I wanna do some open cruiser class racing at BMX tracks. Also does anyone know if a manitou 4-way swinger is too heavy for 4x racing. and at plattekill would it be preferable to throw a air shock or a Ti spring on my AC