Adobe Premiere Pro has supported AMD cards for quite some years too now.
It supports the M370X GPU just fine, it's just that the gains over the Iris Pro (which has amazing OpenCL power for its TDP) are negligible to non-existent and are not worth $500. You find a similar sort of trend when it comes to most GPU-based tasks that are not gaming: the M370X is only marginally better and causes the heat and battery life of the machine to enter a different category.
I wish this wasn't the case and I hope that Polaris can help change the GPU equation on Apple machines.