If it has a tracking number, and I can drop it in a cache and track it's movements, then it is related by virtue of being a travel bug.
We don't require that hitch hikers that have travel bugs attached be related to geocaching, so when I buy a coin, I don't look at it's relevance to geocaching, I look at the design.
Trackable coins are travel bugs. That is the relation to geocaching for me.