Does MOXy support non-string @XmlID in version 2.6.0?
Yes, it is still supported. In 2.6.0 it is not supported by default, but must be enabled via @XmlIDExtension annotation.
https://eclipse.org/eclipselink/releases/2.6.php
Just annotate given field with @XmlIDExtension. It is also possible to specify system property org.eclipse.persistence.moxy.annotation.xml-id-extension to override default behavior globally.