I think the unis that ask for references are quite strict, but if you have enough of other placements with references to cover their min requirements it should be fine. I would approach the provider again however and explain that it’s not a reference in terms of “this person is amazing” etc but just proof with dates - perhaps write them a set of short questions (e.g. dates, hours, etc) as a guide? Or even a template where they just basically have to sign it.