We want to monitor several Linux systems with CDM probes. Is it OK to register these Linux robots to a Windows secondary hub? I did not find anything in the help documentation regarding mixing the platforms for hub-robot communication.
Yes, you can have a Windows hub with Linux or UNIX 'child' robots and deploy and run cdm on those robots.
Please refer to the UIM Probes Support Matrix for OS compatibility:
DX UIM Probes Support Matrix