Hi Martin,
Yes it could be compiled with CUDA support, however not all devices are supported for now by CP2K. Check CP2K installation guide: https://github.com/cp2k/cp2k/blob/master/INSTALL.md
Also you could check which parts of CP2K for now are ported into CUDA:
https://www.cp2k.org/gpu
Performance of the QM/MM in any case would be limited by the performance of CP2K. As you see GEEP electrostatics (which is used in QM/MM) is not yet supporting CUDA, so probably you would not gain much from using GPUs, but still you could try.