We do consider our products compatible with GPUs that were not built into Macs by default.
We only test our products on default Apple systems.
The combinations to account for in regards to modified Mac setups unfortunately exceeds beyond our QA resources.
If you have a modified Mac system and are confident your system should be able to use our products, you are free to use a trial installer and test things out on your system prior to purchase.
You are also free to contact Support if you run into issues, but know that because we haven't tested on your setup that any issues you may run into might not be resolvable if the source of the issue is the untested, unsupported setup.