We package LiveOak with WildFly.
If you look at the stacktrace, you can see the class is being loaded via unifiedpush-server.war classloader.
Which means we have to make it available through it. Either by including it in war, or maybe by using jboss-deployment-structure.xml / jboss-all.xml and refering to extra module in $JBOSS-HOME/modules.

It looks to me, the easiest way to enable drop-in deploy on WF is what I proposed.