Yeah, just make a line image in any drawing program, delete the white background making it transparent, save as a .png, bring it into Vegas, and use a black box to cover it, then slide it around with pan/crop to reveal the line.

If you need the entire route visible, then take a snapshot from the preview box, and draw the line on a layer but don't flatten it until you delete the map, then bring the line into Vegas and do the same thing.

You can use track motion too to move the mask, maybe easier.

Remember: "A transition is a moving mask"