In case you want your exporter to be able to assign attributes to exported entities based on some custom data in your DCC tool, then beware of the SetAttribute method of the Ge2Virtools. In case that you assign an attribute that has no parameter, the Ge2Virtools lib will create you an attribute with a parameter of a type from the font system anyways.
I send that issue to Virtools support over a week ago, but got no answer. I guess they are in holdiays or again they don't have enough people to handle all the input and wait time is 2 weeks (we had that quite often in the past).
So what you got to do is, reimplement the SetAttribute method and check if the type string is empty. If so, use
att = am->RegisterNewAttributeType(attributeName, CKGUID(0,0));