Well, the interfaces are similar, but they are quite different in use.
ACID has tools for beat-matching audio loops so they play in time with each other. That's its primary purpose. You can record a stereo track into any loop projects you create, and you can import a digitized video to make scoring videos with ACID easier... but you can't edit the video at all.
Vegas is a video and audio editing application. It doesn't do looping, but you have tons of control over the video and audio data -- tools to generate transitions, fades, etc. applied to the and audio tracks, and you can record multiple tracks at once right into it, not just one, so it's suitable for recording a live band.