After banging this around for the majority of the day, and with some help from a fellow dev (LunarRaid), we were able to determine that when loading a starling-swf into another starling-swf via an AS3 Loader object, the only combination of project references that would work is if one or both references the Starling source files as opposed to the Starling SWC file. If both references the SWC file, we would get a Type Conversion error to starling.display.DisplayObject on the resultant loaded object when attempting to add it to the loading swf's starling displaylist via addChild.
What is it about the SWC that made the class definitions and super classes unrecognizable when matched to another use of the SWC?