The definition of HD for DVDs is not related to HD as in HDTV. DVD players which can play HD mode have been the standard for a long time. When single layer DVD were what was available for Movie DVDs, they were recorded in Standard Play mode. They could get about 2 hours on a DVD, which fit most movies. (Some longer movies were issued on double sided DVDs which had to be flipped.) For a number of years the double layer DVDs have been the standard used for movie DVDs; they are now recorded in the HD mode. It provides a better quality than before.
If you use the "Fit to Disk" and keep it to around an hour, your disk will be recorded in the HD mode. Except if the original movie clips are in a lower mode, they are left alone.
As to my above method, I have built several disks which have three hours on a 8.5Gb double layer disk. They (including the menu) would as expected in four different DVD players we have. They include a couple of cheap ones and a Blu-Ray player.