Yes but keep in mind like regular DVD, you will probably need to compress them. You certainly aren't going to get
HD DVD quality if you put the whole season on one HD DVD. Image size grows as capacity/technology does. If you are asking whether or not you could fit your existing DVD collection on an HD DVD then yes, you probably could but just because you are putting it on an HD DVD doesn't mean that you will have HD DVD quality. So really all you would gain out of the conversion is the convenience of having an entire season on one disc.