Well, for all the complaints with nasty adjectives, I'd like to suggest that it is 'best practice' to export time stamped BW, and match that up in in a video editor. Otherwise, I'd suggest just handing the client the BW.
Don't get me wrong...
The ability to import video into Sonar is a very welcome feature. The ability to export video from Sonar is really handy for a one-off knock outs. I don't expect neither DirectShow nor MediaFoundation to be broadcast ready, nor do I have a problem with that, nor Sonar using it.
I would think that clients contracting for a score, get just that - a time stamped music track, and maybe a
reference only video with a music track applied (as a
suggested mix) by the composer. The client is going to import the music track in their video edit system anyway.
Now, if somebody is expecting a scored and finished video, trusting you to compose a music track, mix it together with any video audio, and produce a finished video product, you're talking a while 'nother animal, because you're talking about a two more workflows than you agreed to. You might just be leaving money on the table.
You can certainly ask for a specific format for you to score to. Of course, if the client insists on giving you a format that isn't easily supported by Sonar (and using .mov's on a PC certainly qualifies), you have an opportunity to charge a tad extra for conversion. It's certainly not an unreasonable thing, the client is just as capable of doing that as you are, and he may save himself a few bucks by doing it himself. If he is imperious, does not want to give you a format you can work with, it is more than likely he can easily afford a conversion charge - getting your way cost money and he's used to it.