Yup, you can install the PMD extension for JDeveloper via the built in "Update Center" thingy; here's a screenshot:

Setting it up involves creating some configuration files. There's an XML file that describes how the extension hooks into the IDE - that's extension.xml. There's another XML file that contains metainformation about the extension - version numbers, author, etc; that's bundle.xml. Finally, there's an XML file that JDeveloper can use to automatically install extensions; that's center.xml.

Once all those are in place, you can knock together an Ant target (see the bundle target in build.xml) to rebuild/deploy new extension versions and you're off to the races.

Thanks much to the Oracle fellows who helped me get this thing working, especially Shay Shmeltzer, Brian Duff, and Olaf Heimburger. Olaf actually updated the extension to work with recent JDev EA releases; I give him mad props!