In this case, the Plan Administrator is the Plan Sponsor. If both the Participant and the PNHS would both submit affidavits that they were never married, then the PA would be more than happy to allow the Participant to receive the lump sum distribution. The PNHS seems determined not to assist him for whatever reason (at one point the Participant stated there were restraining orders against one another).
It's a well-funded Plan, and the benefit is relatively small - the only risk, as others have pointed out, is a future claim for survivor benefits. With all the information on file, including the mistruths, we are at a standstill - I think we are in a place of no return, with respect to accepting his word that he was never married.
A letter outlining the PA's position/providing his options (including a J&S annuity with his 'spouse' as beneficiary) was mailed to him a week ago. If he protests, we will end up denying his claim for the lump sum distribution and advising him of his right to file an appeal. It may prod him into rethinking his position.
Thanks for your consideration and responses.