I installed Xfce in Ubuntu 14.04, but the network manager icon disappeared. When I run
sudo nm-applet, the icon shows. Not only the network manager but also the power manager and fcitx icon disappeared. fcitx is a Chinese input method.
For the benefit of further readers having the same problem I would like to note that I managed to get the indicators to show up in the xfce4 indicator area without using the indicator plugin.
I fiddled with the settings, but I think the key point was to deactivate the gnome indicators that I marked with red in the screen shot. I reckon these are gnomish programs that might indeed need the indicator-plugin. As can be seen at the top right of the screen shot, at least the network manager and the power indicator appear. Whether there is something special for bluetooth in xfce4, I don't know.
sudo su nano /etc/xdg/autostart/nm-applet.desktop
Go down to the Exec line.
Change the entry:
nm-applet to dbus-launch nm-applet
Save the file -- Control + O
Close nano -- Control + X
Login and you will see that the n-m icon is now back.