I don't think it is, as to be 'grey' it has to be outside the terms of agreement between the buyer and the manufacturer (I'm strictly talking used cars here). That's null and void with most vehicle imports and it has to be traded between re-sellers before the end user. It also also has to be a lower cost alternative, but when you are buying a restored specialist vehicle (for example) it would often cost more than the manufacturer charged when new. Buying a used car (sometimes built decades ago!), that was sold initially via the manufacturers approved distribution channel already, then sold on via a private individual I wouldn't say comes under the 'grey import' umbrella.
I think they actually used to call selling of used goods the 'green market' in some cases.
Its a bit of a grey area. Ahem...