I haven't found any info on this. Should you minimize the Vegas window when rendering? Does the constant refresh of the screen slow rendering times? Would minimizing windows free up resources for rendering?
I don't think it will speed anything up. You can test it if you like.
As for resources, I do not think it will make any difference. Vegas seems to update the preview window on a time and not frame interval and that bitblt (bitmap screen write) should take negligible time.
The screen update is a nice way to be able to tell if a "render as" has hung.