you can:
--telemetry      [=ip:port]. Starts telemetry server. Telemetry data           
                     can be accessed using a web browser(http) or by json-rpc.     
                     If no arguments are given the server listens on               
                     127.0.0.1:2222 - Example: --telemetry=0.0.0.0:2222           
                     Valid port range [1025-65535]

yes. you can use the --dev to specify which devices to use.
so just run zm twice with different pool configuration. in the first use parameter "--dev 0 1 2" in the second "--dev 3 4 5".
for more details run "zm --help".

In my case gpumanager was rewriting xorg.conf. You can check the logs: /var/log/gpu-manager.log

I solved by disabling gpumanager at startup adding nogpumanager in grub loader.
See https://askubuntu.com/a/732004 for details