Google Chrome, like Safari, uses a separate process to sandbox plugins. When plugins implement a full screen mode, it's these separate processes that become the active application.

Beginning with version 1.20, Remote Buddy also detects these separate processes and doesn't switch to another Behaviour. I've just (re-)tested this successfully with Remote Buddy 1.21, the respectively latest versions of Chrome and Safari and a YouTube video in full screen mode.

If you add custom actions to the Safari or Chrome Behaviours, please be sure not to target specific applications with your action, as both Safari and Chrome aren't the right addressees when a plugin runs in full screen mode. Instead, you'd need to send any key presses to com.apple.WebKit.PluginProcess (Safari) or com.google.Chrome.helper.EH (Chrome) respectively. You increase chances of your action to work in both full screen and non full screen mode when you don't use the option to send key presses directly to an application (so it's posted as regular keypress event that goes to whatever application is currently front most).

Best regards, 
Felix Schwarz