The way it worked for me was to render out using the HD Blu Ray template in Vegas.
then open up DVDA, and create a Blu Ray project.
Then when ready to burn change the destination media to DVD and lower the bit rate from 25 to 18 .
(Make sure youre content is less than 4.7Gig).
I am doing this from memory, but that was all there is to it as far as I remember. (other may chime in if I'm off)

I do remember noticing slight artifacts on fast moving video, I thnik due to the lower bitrate. If you keep th ebit rate at 25, many players will not be able to play them.

Ted