There was a bug prior in RHQ 4.2, and possibly for a while, such that Embedded WAR resources (Child resources under an EAR resource, like coregui.war under rhq.ear) had an invalid "Filename" plugin config property value (and similarly incorrect "Path" trait). The value was not a true path, it had extraneous information appended. This causes problems for the new Drift support, which relies on the Filename value being correct, the proper path to the embedded war directory. The problem has been fixed but that means to apply a drift definition the existing resource will need to be re-imported, to get the proper value assigned.
After further discussion, we won't be supporting drift on embedded web apps, so the documentation should state that.
So noted: http://docs.redhat.com/docs/en-US/JBoss_Operations_Network/3.1/html/Admin_Managing_Resource_Configuration/drift-config.html#drift-resources