For now caskroom.github.io/search works but I didn't know about it until today and the project seems small with only 10 Github stars.
It's maintained by the 'official' brew cask maintainers; /caskroom/homebrew-cask has 10.6k stars, so I wouldn't worry - why would I star their website repo?
caskroom.io is listed on the team page on Github, so it seems like it's just an oversight.
You could always let the maintainers know with an issue - though if they're not aware already I doubt it will take long :)
EDIT:
Actually, check out this commit: https://github.com/caskroom/caskroom.github.io/commit/3aa01f...