If you want to eject CD/DVD drives, you can create a launcher to the following command:
eject
and lock it to Unity launcher. This works if the tray is empty, too.
Creating a launcher
Create a new text file with the following contents:
[Desktop Entry]
Name=Eject
Exec=eject
Icon=cdrom_unmount
Terminal=false
Type=Application
StartupNotify=false
(you can replace cdrom_unmount with media-eject or any icon you want)
and name it Eject.desktop. Right click that file, select "Permissions" and check "Allow executing file as program". Then you can drag it to the Unity Launcher, and get something like this:

Just click on it and the tray will open.
It's not possible to show Unity CD/DVD drive icons if there is no disc in the tray, so this is the best way to get a Unity eject icon.