I thought I would add some follow up. I spoke with another person at Cajun. They do not recommend milling a Shadow 2 slide to allow the factory rear sight to remain in place because it leaves so little metal between the ejection port and the RDS. They think eventual failure of the slide is likely with heavy use. Other slide millers will do it. So, it's a difference of opinion about whether its appropriate.
The rear sight dovetail on a Shadow 2 sits further forward than on some other CZs, like the P-01. This results in less space betweeh the dovetail and the ejection port, leading to the issue with milling.