How is it possible to have global hotkeys in OSX?
You can assign a shortcut to a script like this:

tell application "System Events" to tell process "VLC"
    click menu item "Step Forward" of menu 1 of menu bar item "Playback" of menu bar 1
end tell


For example save the script in ~/Library/Scripts/ in AppleScript Editor and then use FastScripts to give it a shortcut. Or if you have bought the Powerpack for Alfred, you can create a workflow with a Hotkey trigger connected to a Run Script action.