There is no way that Hughes is better than Serra on the feet. Matt Hughes has never done anything on his feet. Also, I've stated this in another thread, Matt Serra's jiu-jitsu is overrated in an MMA context. Matt Hughes jiu-jitsu, while probably not technically as good as Matt Serra's, translates very well to MMA, probably due to his strength and control. I think Hughes is going to get the fight to the ground, control Serra for a couple rounds, tire him out and then probably pound him out in the 3rd or 4th.
Serra's best chance, like in the GSP fight, is to catch Hughes early, before he has a chance to take it to the ground, because once there, he just doesn't have the physical size and strength to hang with the big boys at WW.