I ran into a substantial problem with the way Netbeans packages up Java programs into native Mac Apps (For those who aren't familiar, Netbeans can bundle your Jar file with a JRE so you have a completely self-contained App. Clients don't even have to have Java on their computers to run it. The whole process is explained well here).
The problem I found was that the apps Netbeans produces completely ignore JavaFX Preloaders. I think it's because of the slimmed down JRE that gets added in. I couldn't find any solutions online and wanted to post one here for anyone who runs into the same issue.
Here's what you have to do:
In the above, substitute YOURAPP for the name of your jar file, jdk1.8.0_05 for whichever version of Java you added in step 4, and ICON for the name of your app's icon, if it has one.
There you have it! The app should run as intended, preloader and all.