I happened to notice OW 5.5.2 B2 was available today due to a listing on VersionTracker:
http://www.versiontracker.com/dyn/moreinfo/macosx/3253
However, using "Check for Update" in Beta 1 showed that the installed version of Beta 1 was "up to date" instead of determining that Beta 2 was available.
I don't know if this is a "feature" of Betas, a bug in Beta 1, or if there was some server issue, but I've since downloaded Beta 2 from OW's site. I seem to recall that, in previous Betas, updated Betas would be seen by "Check for Update." Hence, this report.