I mean theoretically that shouldn’t affect the quality of your video, but most people on here, myself included, advocate making a self-contained QT movie. Bring that movie into Compressor, apply the DVD settings, turn on Frame Controls and adjust the Resize filter to Best.
I was just in similar predicament except I had H.264 720p footage. After reading a lot of forums and what not, there doesn’t seem to be one solid workflow to put HD footage onto an SD DVD. There are methods that work for some people that don’t work for other people. Depends on what format your source footage is, how many effects, the type of content (sports versus interviews), etc.