I seem to have answered my own question (I think)
In jboss-service.xml I switched my URLComparator from the default DeploymentSorter to PrefixDeploymentSorter, and then prefixed deploy/scheduler-service.xml with a single numeric digit - i.e. it's now named 9scheduler-service.xml.
That forces it to be deployed after all the un-numbered and lower-numbered objects in the deploy directory.
It seems to work...