Because the ROCm stack even with the coming 1.8-beta does not support Ubuntu 18.04 I went ahead and tried AMDGPU(-PRO) 18.20 as a last resort before segmenting the homogenous cluster and downgrading AMD nodes to 17.10 or even remaining on 16.04. After installing the driver packages manually (because the installer script fails due to missing dependencies of i386 packages (why is there not option to omit 32-bit support on a 64-bit node??)), the module amdgpu fails to load. kern.log is attached.
How should the drivers be installed, because the "Linux installation guide" does not work.