Hi Matt -- You can search layers that are configured for search in the map. Please see Configure feature search—ArcGIS Online Help | ArcGIS for details on how to do so. Would that enable the type of search you are looking for?
Yes, that is what leads me to believe it should work in collector, as it works in AGOL when I set up the webmap like that. But when it gets to collector, I do not see any way to change the layer I want to search on.