The plan can definitely require these things. They are requiring nothing more than the employee prove that he has the family members or dependents that he or she claims he is. Insurance is a contract; insurers (including self-insured employers) may put pretty much any terms they want on buying or receiving insurance, and those terms can include proving eligibility. The insurer does not need to take a would-be-insured at their word that someone else is a spouse, for example, and therefore covered: they can can ask for proof. It's no different than having to provide proof of the value of a car being insured, or a house being appraised to prove value, or taking a medical test before receiving life insurance.