Most people who race the DH hardtail class are on dirt jump style bikes rather than XC hardtails. You could do it on an XC hardtail, but make sure you can lower the seat way down or you're gonna die on the jumps.
It would be possible, but it depends entirely on your skill level. Not saying you couldn't do it, I have no idea how good you are at DH. But seeing as your asking if you could do it on an XC hardtail, I imagine you don't really know what you're letting yourself into. But yeah by all means go for it! :P
I've done a few dh's on a fs bike, in addition to countless hare scrambles, enduros, Mx races. I'm familiar with downhills and I do have a pretty solid skill set and background with, but I've never been to sea otter, and I've never been a DH course on my hardtail, although I favor DH over XC.
Might just have to bring the gopro if I decide to give it hell
It sounds like you know what you're getting yourself into and have the necessary skills. XC bikes can be setup a lot of different ways. If you have a 29er with a 4" fork and wide bars and you can swap a shorter, taller stem on it will be fine. A 3" fork, narrow handlebar, 26er will be a handful.
Well then it's going to be a handful then lol. It's not a fully decked out XC bike...my bars do have rise in them lol. I know it'll still be a handful, but I'm going to need to do something to keep me entertained until Sunday haha. I appreciate everyone's help and/or suggestions. Next year I'll just have to be prepared and have two bikes!