Gordon, if I were you I would burn a true DVD-Audio disk. As you probably know, Audio DVD Creator does not make Audio DVDs but Video DVDs with 24-bit audio tracks. These just work with 24/48 or 24/96 so you have to upsample. With DVD-A you just could burn the files "as is" and so archive them.
Anyway your question is about letting Audio DVD Creator upsample alone and drop the original 24/44.1 file after that. Well, I wouldn't, because you have no reliable info as to the quality of the upsampling algorithm used by that soft. I tried a comp and the computing time it took to upsample is rather short, which is somewhat unsettling. My wild guess is that upsampling is done in the 24-bit realm, yet for a clean job to be done, it should perform it in the 32-bit realm.
If I really had to burn a DVD-V, what I would do is I'd use a good app like SF8, Audition 2 or even Audacity, convert to 32-bit depth cleanly, upsample, then dither down to 24bits before burning.