I made some progress today in resolving my issue. I created a feature layer view of my feature layer. I then made a new AGOL map and added the feature layer view. This new map now shows up in Collector. While not ideal, this works. It is odd to me that the online map that is generated by the Workforce app. does not work in Collector - even though I have the integration settings configured and an editable layer. I tried replacing my feature layer with the feature layer view in my Workforce worker map. The Workforce worker map still doesn't show up in Collector. I don't think there's a way for me to change the source of the Workforce worker map to the new Collector map in the Workforce app. It only lets me configure the existing map. So I will have to maintain 3 online maps instead of 2.