How about Sonar’s video view and the thumbnails in the video track?
(from the Sonar manual) Open the Video view by using the Views > Video command or by pressing ALT+SHIFT+2. In addition to the Video
view, there is also a Video Thumbnails pane in the Track view
Sonar has limited video render capabilities, but you can build a score, export it, bring it back to vegas, then render it.