I have macpro running el capitan 10.11.6, with AMD Radeon HD 7950 3072MB which, last time I checked was a supported GPU. PS 2017 claims there is a problem with the driver. The driver is an apple driver - no way to "reload" it. The first time I ran 2017 after installing - I got this error. I rebooted and restarted PS and it seemed ok with it. Now it consistently claims there is a problem with the driver. So is that card supported or not?
I went into Google and looked at the cached page
AMD/ATI Radeon: 5000, 6000, 7000, R7, R9 series, 7950 Mac OS is listed but for CC 2015.
I would think if my MBP with an Intel HD 4000/1.56 MB can handle CC 2017, your card is capable.
As a CC Subscriber, you can install and use an earlier version of Photoshop. CC 2015.5 for example and see how it performs.
A card can be supported but not work because of driver problems. Drivers sometimes get broken rather than fixed by updates to the driver or system. Actually you don't tell us what the error is. Please give details.