Just discovered the problem after having issues with Gallery Remote (another Java program) earlier.

SOCKS proxy settings in OS X.2.3 screw with Java programs that use the network. Gallery Remote was spewing all sorts of strange errors into its log, but once I unchecked the SOCKS proxy in the system preferences, it worked fine. I opened JEmplode, and it found my empeg right away via a network broadcast.

Also, once I disabled SOCKS proxy support, JEmplode was able to detect the HTTP proxy settings properly, and pull down Hijack 301.