What I think I see here is a fundamental misconception on how video on the web works. This may surprise you, but framerate is irrellevant! Try it for yourself: make some short videos in standard (24/25/30) and 'silly' framerates (like 13.5 fps), use the same Flash video player (component, or your own), and you will see every one play back at the correct speed, without any modification to the player.
Modern webvideo is a stream. You can't even access frames, i.e. there is no "video.gotoFrame(18)" for instance. In a video stream, you can only access time.
Fixed framerates only apply to hardware devices like television sets and its associated media feeders like DVD players. In NTSC countries (USA, Japan and others) it's 29.97, in PAL countries (Europe and others) it's 25. You also need to stick to certain sizes. Webvideo is a much more flexible beast in every regard.
As I said, on the web any framerate will play back at its correct timing. In Flash you have one exception: the possibility of putting video in the Timeline. Here the Stage framerate and video framerate need to match to obtain synch - but you can't set the Flash movie framerate to numbers like 29.97 anyway. More importanltly: this is not the recommended practice either.
If i was you I'd give the client a movie YOU are satisified with, and then see what happens ;)
Not everything that can be counted counts, and not everything that counts can be counted.