It's not possible to add another look and feel to the drop down in the current version. However, you can change the look and feel of the IDE if you don't mind messing about with properties files a little. Here's how:
1) In jdev, set the look and feel to be Oracle.
2) Quit JDev
3) Edit the file ${jdev.home}\jdev\system***\settings.xml in notepad
4) Search for the string "OracleLookAndFeel". Replace the string oracle.bali.ewt.olaf.OracleLookAndFeel with the class name of the look and feel you want to use.
5) Drop any .jar file required by the look and feel you want to use into ${jdev.home}\jdev\lib\patches
For future reference, you'll get a quicker response on JDeveloper questions in the JDeveloper forum.
Here is how you can add new L&Fs to the drop down list. (Instructions are for Linux , as I use Linux, but they will work for Windows too)
Add the L&F jar to <path to JRE>/lib/ext (or <path to JDK>/jre/lib/ext). Then create swing.properties (if it does not already exist) in <path to JRE>/lib (or in jdk...) with following lines:
Note that I retained default example L&Fs that normally come with the JDK/JRE (depending on the platfom) and added PlasticLookAndFeel as additional PLAF (Pluggable Look And Feel).
Now it should be possible to choose Plastic L&F in not only JDeveloper but also other Swing apps that you want to use.
Please let me know if this works and also if you have any questions.
This is how I made it to work on Linux (Debian GNU/Linux sid).
I copied the LAF jar file to <jdk>/jre/lib/ext. Then created swing.properties by hand (as mentioned in the previous post).
I backed up my ~/jdevhome and let JDeveloper create the new ~/jdevhome. The JDeveloper started in default L&F (Metal for me). I looked in the preferences and it showed all the L&Fs I had set up in my jre. At this point there was no settings.xml created. I selected the Plastic3D L&F and exited. Now it created settings.xml with following entry.