I'd think a vehicle would have to be equipped with a factory towing package to make one of those wire harnesses work.
I say that for a couple of reasons as it relates to the VX.
First, to even be able to plug one of those harnesses in, the vehicle would have to have a breakout section in the factory wiring harness for that adapter to plug into without splicing, and second, because the VX wasn't recommended by the manufacturer for towing in the first place, no towing package was offered (AFAIK anyway).
Since you'd be splicing into the wiring inside the vehicle, you shouldn't have any issues.