" I have had double coverage through my own and my spouses
employers and the "secondary" (my husband's insurance program) has covered most
of my 20% co-pay for my primary insurance (after the deductible on the secondary
policy has been paid). Most hospitals and doctor's offices' forms ask for
information on secondary coverage. "
This makes sense. If you pay for dual coverage and are
eligible to do so, you should be able to use it.
However, to the original question, whether or not you get
payment in lieu of benefits you decline will be up to your individual employer
and the local laws governing that employer. For instance, if a state
mandates no discrimination based on marital status and an employer paid full
premium for married employees, an employee who was single would receive the
difference between their premium and the married/family coverage.