Checking SL's front page it says their latest releases are 5.5 and 4.8. Checking their FTP directories, it says 5.5 and 4.8. The document you linked to says, "Linux ALPHA" so I'm guessing it is an alpha release just like they have released test releases for 6. With CentOS 5.6 supposedly only a few days away... that seems more advanced than an alpha release but I don't want to count those chickens before they are hatched.
Oracle was my bad. I hadn't seen their 5.6 release noted on distrowatch.com and didn't hunt down the info on their site.