Nuendo will write audio to a video file, but you can't do any video editing.
I think Nuendo is more powerful than Vegas Video in the audio dept. I much prefer Nuendo's way of doing things when it comes to fx, inserts, automation, etc. However, one of the places where Vegas Video shines over Nuendo, is that you can have multiple file formats, bit rates and word lengths all on the same track! That saves so much freaking time!!!
I do like Vegas, though, and I also like that Vegas Audio, Video, and Acid all share the same interface. Makes for a good all around project environment.