How can I view packages from a specific repository?

You can examine the package list file(s) from that repository, they'll be in the /var/lib/apt/lists directory with names that start with the domain for the repository and end with _Packages.

It doesn't look like that repository supplies a Release file. If it did, aptitude has support for using the Origin specified by a release file as a search term. I have a Mint repository as a source in addition to the main Debian repositories, and I'm able to limit the packages that aptitude shows to just the ones from Mint by typing l?origin(linuxmint). But without a Release file, I don't know of a better method than just looking at the raw package list file.