Honestly I can't be totally sure, but he was taken to and from by a coworker I trust not to mess with me like that, and the manager follows store protocol to the letter, which is a problem when the store protocol is nonsense, but if it dictates vet visits, vet visits will happen, at least in my experience. In the past few months we've had a few guinea pigs that needed vet visits and meds for minor issues, and that happened pretty timely and the meds were followed up on, so I've got that experience to draw on.
I definitely can't fault you for being wary though, if it wasn't explicitly in the store protocol I wouldn't trust the GM an inch to follow up on health concerns, and I know there's loads of people who would disregard it even then.