The ArcMap based method does seem to preserve the center of the symbol where I want it without adding any unwanted artifacts when I export to emf files.
I now will have to look at transfering the symbol configuration steps into ArcMap using the drawing tools, since I need to arrange the core symbols into possibhly up to 1,150 configurations (using at least 8 different arrow designs and 5 non-vehicle symbols used as singletons or in a paired combination with day/night and orientation variants). The base symbols are reasonably simple and I should be able to import them from AI from the base emf files I have made.
Thanks for making me aware of ArcMap's emf export capabilities.
Just another note for anyone wanting to do this. The Data Frame does need to contain one layer where all of the layer features are positioned outside of the bounds of the Data Frame so that they are not visible. This is necessary to get rid of the label in the center of the empty Data Frame that says "Layers", which only disappears when the Data Frame actually contains at least one layer.