Thanks for checking. I rolled out a patch to move the population of the JS variable DTMdataLayer above my DTM include and that rectified.
As a follow up, AEM ContextHub tool and integration in this fashion. I used the "Customized ContextHub Data Layer" option and added my data layers definition to the bottom of the default and then saved. I entered DTMdataLayer for the "Data Layer Root" in hopes that this tool would automatically expose these variables. Perhaps saving a wee bit of time when defining my data elements, as they would be exposed in the DTM?