Hello,
That's correct, the main reason iMC would currently have issues with ZTP on AOS-CX is due to Telnet being required with the initial configuration. A future version (likely an upcoming patch release for E0706) should include a change with which iMC will automatically use the CLI access protocol specified for the ZTP device during the entire process, rather than after the configuration deployment is done. That should allow ZTP to work for AOS-CX devices as well.
If you need more info about when this (and ZTP support for AOS-CX in general) would be implemented, please check with your HPE Sales/Account Manager contact.