You can put HD content onto a dvd, it just won't play in a standard dvd player. The dvd would be used just for data storage, in which case the only thing that matters is if there is enough space.
For example, burning the hd content on a dvd to playback on the ps3... Ohhhh, I wonder which is quicker now, splitting an 8gb show to 2 4gb pieces then dumping it onto a fat32 usb external drive or burning it on one run on a dual layer dvd.