Hi.
The cooling head of the M22 is made out of copper. The radiator is made out of aluminium.
So it is safe to use.
Question is however why you wanna use LM in the firstplace over regular thermal grease.
The 2700X uses solder and not thermal grease like Intel so there is no benefit from a delid. And using LM between the waterblock and the IHS will gain you maybe 1 - 3 degree celcius.
https://www.tomshardware.com/reviews/thermal-paste-comparison,5108-8.html
So to be honest mate. I would just go with regular paste like Thermal Grizzly Kryonaut.