Screen9 support VAST tags for advertising. More specifically our players use the Google IMA Flash/HTML5 plugins to play the actual ads.
Make sure the tag plays in both the test page's HTML5 and Flash players, in order to ensure smooth playback of ads on all platforms.
Note that Google's test page wants the VAST tag to be HTTPS to test it. If your tag is HTTP it is usually enough to add an S to the protocol since most ad platforms should support HTTPS.