“You can leverage the power of Java by using any Java library within a JavaFX application. This way you can preserve your investment in Java and use JavaFX to build engaging visual experiences.”
The statement above is in the JavaFX FAQ at 4.4. And of course you can use any java library available without any changes.
However try to bind a variable form a simple java class to any value in a javafx class and you will see that integrating java into javafx is not as simple as it seems.