1)Since I have an option to render into avi-cineform from my NLE (vegas) if I downsize a 1080 to 720 is there a quality difference between Link or the NLE provided both are bing rendered into Cineform AVI
2) I then wish to make a DVD size version from the 720. Is it better to downsize it in the NLE render to cineform avi or export as 720 cineform avi and run it thru the resize in HDLink?
I have Neo

Try it. In the past HDLink scaler had edge, as it always uses a Lanzcos 3 scaler, yet I seen a lot of improvement in the NLE also over the years.