Well yeah, just like in AE you can do reveals by animating Motion's masks over time.
But an easier method is to use the Write-On behavior: Add Behavior>Shapes>Write On
And you can also use the Sequence Paint behavior if your using Motion 3's new Paint Strokes feature.
And there's even a script for converting Illustrator shapes to Motion shapes:
http://www.motionsmarts.com/downloads.html :)