Preferably, you should stick to one system or the other, rather than trying to mix and match. Luckily, if the only thing that is mixed is drill sizes, then there is an easy fix if you have already done the work to make the drawing, and you don’t want to re-draw the part. Because tool paths for drills are off the center of the hole, changing drill sizes won’t change the tool path, it will only change the RPM and feedrate of the tool. You can convert the imperial holes to metric on the CAM software and simply use the imperial drills you want to use when cutting the part. The tool path won’t differ if the only imperial feature is the hole diameter, and the CAM will be able to calculate the correct RPM and feedrate if it has the converted metric diameter.