I found this article saying OpenJDK uses epoll on linux, but does anybody know if Selector implementations use kqueue, dev/poll etc over traditional polling where available?
Yes it does. java.nio.channels.Selector.open() returns different implementations depending on your underlying operating system. Eg. If you are using a JRE from sun/oracle you will get:
Windows
sun.nio.ch.WindowsSelectorImpl
Mac OS
sun.nio.ch.KQueueSelectorImpl
Linux
sun.nio.ch.EPollSelectorImpl
Solaris
sun.nio.ch.PollSelectorImpl