Good point, thanks for reminding me a about this.
We had a similar problem with our own usage of JBoss Logger: https://issues.jboss.org/browse/LOGTOOL-105

Sadly I hadn't thought we would be causing the same pain to others via hibernate-jpamodelgen

N.B. there's an easy workaround: officially @Generated isn't part of javax.xml.ws.annotation (that's just its temporary home) but it's also available as an explicit dependency:

<dependency>
    <groupId>javax.annotation</groupId>
    <artifactId>jsr250-api</artifactId>
     <version>1.0</version>
</dependency>

I agree we should make it easier though; likely applying the same trick as we did for Logger.