Although by definition using taxis is not allowed in classic%, would calling the taxi company in order to spawn a taxi nearby to use it as a vehicle count against this rule or not?

I ask this since this would be used once in epsilon%, after going up the east coast of the map for hidden packages and before doing the third epsilon mission.

No, it's only utilizing the fast travel.

The rules text is in the process of being updated to make this clearer, Velo is corrected.