Really? It's paid by the taxpayer, either by paying directly to the government for those not receiving SS benefits or by choice, or it is withheld from benefits. Either way, the taxpayer is paying premiums out of otherwise available resources.
It hasn't been an issue in years and won't be challenged. IRS Chief Counsel issued its legal interpretation for use by IRS personnel back in 2012 that addressed this and stated that Medicare coverage for the self-employed person AND spouse are eligible. Chief Counsel Advice (CCA) 201228037 http://www.irs.gov/pub/irs-wd/1228037.pdf
JoA article from 2012 in explanation. https://www.journalofaccountancy.com/news/2012/jul/20126051.html
Also, it's now clearly addressed in the Form 1040 instructions for line 29 that this IS eligible for inclusion in the calculation of SEHI.
IRS statement on use of CCAs from IRS website:
If by second policy you mean that a TP has 2 (non-medicare, non-medigap) health policies, then there are specific rules and 2 separate worksheets need to be completed for the SEHI.
If, by the above statement that you are referring to MediGAP as secondary coverage to Medicare, that is eligible for inclusion in the SEHI calculation, as are other policies for dental, vision, drugs, and long-term care.