Gary,
You've done what was asked of you, but it is a mystery is why the audio portion of your video is not carrying over to Keynote. There are no setting to tweak, no volume controls to change - if it sounds right in the Photo app it should also sound right in Keynote.
How are you importing through iTunes? Are these stand alone videos or did you place them in iPhoto first (on your Mac)?
At this point I can only suggest you try a few things:
If you have Keynote on a Mac, try placing the video on a slide on your Mac and play it to see if it sounds in Keynote - there are volume controls on the OSX version of Keynote that are not available on your iOS device so you can check that the volume is all the way up. My thinking is that if you imported the new Keynote via iTunes and the video is already embedded (and the volume controls on the movie object (Quicktime Inspector > Volume) is set to play normally on the Mac) then you import via iTunes, all the video attributes should copy over. Then you can open the new keynote and COPY the video and PASTE in your older presentation and try the new version.
If no Keynote on your Mac, if you have iMovie on your iPad and can open the video in iMovie and it plays, you could try exporting a new copy of the video from the iOS iMovie to the Camera Roll and try placing the new version on your slide in iOS Keynote. You do this in iMovie document view (thumbnails & marquee visable) - select the video and Share (icon of box with arrow pointing outwards) > to Camera Roll and try placing the new copy of the video in your Keynote presentation.
Try those and let us know.