I would like to know if Radeon 7 graphics card will work with the old mac pro ( tower ) with update to Mojave with future driver updates for radeon 7 ?
Some might some may not. Others may with a bios update. Also some model need a custom cable adapter as the apple cable isn't standard. Apple gives zero info on this. Many mac forums have this information if you search.
If you would like to take the guess work out you can buy one from other world computing they are macsales.com been buying from them for over 30 years myself. I have used macs since their inception. They have a model that claims full support for the mac pros and is mac compatible. You will pay premium for that card, but everything that goes in a mac is a premium, unless you figure out what PC product will work on the cheap.
Anyway here is a link to that card: