No OS X firewall or 3rd party blocker. I was able to get it going though.

Working under the assumption that something from the original Plex was getting launched and confusing the situation I turned off the StartUp for everything Plex and Remote Buddy.

After I relaunched there was still a PlexHelper running in the background. A search of the hard drive turned up copies inside the applications but also in ~/Library/Application Support/Plex and also Plex Home Theater.

I moved the Plex folder out of Application Support and re-launched. No PlexHelper at startup now.

I was then able to bring up Plex/HT and Remote Buddy looks to be working well for me.

At some point I was using Plex .8 I believe. Also in Plex I had the option turned on for "Remote Always Available" or the like so some combination of these may have contributed to the issue.

Short version: 
Move ~/Library/Application Support/Plex out of the Application Support directory 
Reboot 
Remote Buddy now controls Plex Home Theater

Thanks for the great product and prompt support!