All I know is that iDVD in iLife05 can burn all types of medias, -r and +r, so I'm guessing that the other more advanced suites can too. But that is just a guess. Plus it depends on what your drive is. Of course, its most likely a DVD-R drive that you have, but I'm wondering if you just tried to burn it and see if the media just works. Otherwise, you will need to find another computer, or an external DVD+R burner to be able to use that media. But the thing is, the clients DVD+R drive might be able to read the DVD-R. DVD-R is more compatible with regular DVD players than DVD+R. That is the reason why Apple went with it in the first place, so you can burn then play on more dvd players than the other type of media. That is if my memory serves me right.
I'm guessing that you want to send the client something that will look like the final product or takes them though the video clips on the DVD with ease. So burning it onto a DVD-R might not be a bad idea. Because you never know, they might take it home with them to play on their home DVD player, or their DVD player in their desktop should be able to read it. Now that I think of it, I have given people DVD-R media with files on it, and they have watched the stuff on an HP PC with a DVD+RW drive. Let me ask her when she gets back, but I do believe it worked.
EDIT: OK she can't remember, so you might just want to post a new thread asking if +R drives can read a burned -R disk.