Do AppIndicators work on Xubuntu?
It should definitely be possible because the indicators are made to be cross-platform.
It appears that someone has developed an xfce panel applet to do provide this functionality: http://goodies.xfce.org/projects/panel-plugins/xfce4-indicator-plugin
It doesn't seem very mature though - its at version 0.0.1, which is the first stable release. It is not packaged but is available as source code.
- There is an XFCE panel plugin that should make it possible to put most GNOME panel applets into the XFCE panel.
- The indicator applet is a GNOME panel applet.
Maybe you can try if 1 supports 2?