Not directly from Flash Catalyst. If you the exact url location of you clips (the actual flv files, not the host page), you can then take the Flash Catalyst project into Flash Builder and swap out your local video for the remote video.
Opening the Main.mxml file in the Package Explorer, then locate the <s:VideoPlayer> tag. Change the source attribute to the full url of your clip. Now republish the project.
A couple of notes: Opening Flash Catalyst 1.0 projects into Flash Builder is a one way trip. Also, you might encounter cross-domain security issues in playing YouTube files.
There is a great set of tutorials about accessing YouTube via Flex at: http://devgirl.org/2010/01/25/flex-youtube-api-and-player-samples/
Hope this helps,
I will keep both of these inmind.