There are out-of-bounds writes in the BLAS libraries for gfx803 GPUs (such as the RX 570). That hardware might work fine for your use case, but there's a lot of failures in the test suites.

I agree that the official support list is very conservative, but I wouldn't recommend pre-Vega GPUs for use with ROCm. Stick to gfx900 and newer, if you can.