I run a site with lots of embeded youtube videos, the majority of which which are created by others. I know the publishers of those videos can enabled adsense on the videos and get a cut of the ad revenue, but are there any options available for the publishers of websites that embed these videos? If not through youtube, is it ok to sign up for pre-roll video ads from another source and play them before youtube videos?
You could try using http://www.AdStract.com They have overlay video/display/software ad's that work with YouTube video players.
Adstract might be the ticket - i have a contract to syndicate pre-roll ads from adap.tv LiveRail and other exchanges, but none of them now allow their tags to be placed over youtube content. They didn't enforce that very well in the past - now they do. There is software that allows a pub to play video tags without video content as well - but sites are getting rejected for that as well.
Given how popular the YouTube player is, it seems very counter-productive that these networks don't allow their ad's to overlay the YouTube player. Anyway, just to say, since I recommended AdStract, they have very seriously went down-hill and I no longer run their ad's on my website.