While reviewing the flags on a Programmers post I found this:
You can clearly see that the post was flagged 5 minutes before the post was Tweeted. While in this case the post remains open, it might not have done and there would have been (another) closed question Tweeted to the world.
Posts with close votes aren't Tweeted so can the same logic be applied to posts with flags?
Yannis raises an interesting point in the comments - perhaps the number of helpful flags raised by the flagger should be taken into account as well. This would mean that a flag from someone with 300 helpful flags will stop the Tweet, while a flag from someone with only 10 won't.
Of course, once the flags have been cleared and if the post is still open then it should be eligible for Tweeting once again.