In my mixed AMD/Nvidia rig. JCE GPU Miner is mining on the Nvidia cards as well as the AMD one.
Doesn't appear to be any way to specify amd or nvidia via command line. Adding -g 0 works for now in my case as the RX 480 is gpu 0.
Jce must work only on amd gpu.
You can create issue and attach sceenshot of miner window.
https://github.com/jceminer/cn_gpu_miner/issues/new