There's no reason for the YNs to even care - it's all transparent to them and there's no requirement or mechanism to explain whether or not a Govt CC was used. Despite the rhetoric/party line, the only thing you really have to use the Govt CC for is when they put airline tickets, lodging or rental cars directly on your card. Everything else is up to you as a practical matter. I have never used my Govt CC "as intended" and nobody has ever said a thing. I ran my squadron's program for a year as the Admin O and there's really no reason to fuss about it as much as some of you seem to be. Use it as you see fit within the bounds of common sense and 99% of you will not have issues.
The provision is "exempt from mandatory provisions of the JFTR" on the orders. If the traveler is exempt than they can freely use their own card for whatever necessary for travel. If the traveler is not exempt, they are required per the JFTR to use the GCC for all transactions associated with their official travel.
That said, and as you know, what goes on in real life is completely different.