Welcome to the Apple Support Communities. You can easily get your slideshow to YouTube. The following article will assist you in the process.
The area you are looking for is: Choose Share > Send To > YouTube
I came across these or similar instructions in the Keynote Help, but wasn't able to make them work when uploading to Youtube, because I tried doing it directly to the Youtube site. I imported the video made with Keynote into iMovie, and then added the soundtrack. I then discovered the ability to upload from iMovie directly to Youtube, and now, with your suggestion I realize the same can be done from Keynote.