It is really a matter of selecting the correct equipment. If head protection is necessary - not just required by a procedure or policy, but actually required to protect against a hazard - you can use a welding helmet which provides full head coverage. The newest technology is a helmet that looks a lot like a motorcycle helmet. It has auto-darkening lenses, and a PAPR blower. The thing is pretty versatile and covers a lot of bases. It provides UV/IR protection, head impact protection, and respiratory protection. They are worth their weight in gold if you are doing a lot of stainless work or in a HCA.
The welding helmets that fit on a hardhat wont fit just any hardhat. It has to have attachment lugs factory-installed. Sometimes these are known as a "fitters' hardhat" although it is worn just as often my ironworkers and other welding trades. They are a lot more expensive than the ten-dollar hardhat that everyone else wears.
Of course, you live in the nuclear world, where the tail wags the dog. Out on Planet Earth, we look at the hazards and provide the PPE for those that actually exist. That is why there is no such thing as PPE "exemption" or "waiver" out here. There is no need to exempt what is not needed. Unfortunately, once you start writing those things, you end up writing them when you probably shouldn't, and exempt PPE that is needed just because someone convinced you that "inconvenient", "uncomfortable", "expensive", "time-consuming", or "not-in-stock at the tool crib" are legitimate reasons to write a different set of safety rules. Don't get caught in that trap. Make them bring the proper equipment to the job.