As a veteran singer, I would never recommend compressing the vocals in the monitor mix. If you find your singer has poor mic technique, fix that with on-mic practice. But it is very important that what comes out of the monitor is what is true. I personally would entertain a drop of reverb on the vocals, but even that can cloud what is really happening in a live situation.
Even if it didn't risk a person's vocal health, it seems like a complicated way to avoid kindly saying "please pay attention to how you're use a microphone".
Even if it didn't risk a person's vocal health, it seems like a complicated way to avoid kindly saying "please pay attention to how you're use a microphone".