The trick is that at runtime, the annotations don't exist anymore. They are only used at compile time to generate "normal" plugin code that the RHQ then sees and uses as normal.
As you know, there is a connected, if somewhat distinct, effort to come up with a common set of management annotations across JBoss products, where I think the JMX management annotations (either JMX 1 or 2) will be considered.
https://community.jboss.org/message/828515
I set off to implement the annotation processor (together with a set of annotations) in an attempt to have a clear set of requirements from the RHQ side that we could then use as input into the above discussion.