The Covenanter position is pretty straightforward on this point, we don't acknowledge the authority of godless governments when they seek to enshrine violations against the moral law as state policy, and David Steele and his party that resisted the so-called "New Light" movement of the Reformed Presbyterians of the 19th century pretty well predicted where all of this was leading. We're extremely small in number, but we have taken a hard-line on anything involving direct involvement with the U.S. federal government due to allowances made in the U.S. Constitution that pretty much paved the way for stuff like this. We're not incorporated, no 501(c)3, we don't and will never provide chaplains for the military, military service is generally regarded as being the same as signing up with Caesar during the persecution of the church, we claim a religious objection to jury duty on similar grounds, and anyone who violates our regulative principles as drawn from the Solemn League and Covenant (including the prohibition on Occasional Hearing and the principles of political dissent) are bound to disciplinary action, including excommunication for unrepentant, habitual violations. In light of all this, any person who would openly condone homosexual unions or otherwise suggest that our ministers perform them would probably want nothing to do with us, mostly because of a laundry list of other things that we don't dignify with a debate.
To answer the OP's question, any legitimate church will not marry anyone who isn't a communicate member in good standing with the church. We generally recognize marriages performed outside of our church if and when families come to us for the purpose of converting (we generally don't re-baptize anyone either unless they were baptized in an invalid fashion such as a non-trinitarian baptism via the Jehova's Witnesses, Unitarians and Mormons), but scandalous people are not married in our church prior to repentance and a period of probation.
I don't think any church can be bound to violate their own doctrines by the civil magistrate, but any church that bought into the notion of sharing a government with pagans, libertines and atheists was asking for a state of being compelled by force to violate their constitutions, and it will eventually happen, mark my words. It's interesting to note that the SCOTUS that foisted this recent decree on everyone is majority Roman Catholic, which is largely unsurprising to me, but I'm sure all of the weekend conservative types whining about this out there actually thought that the RCC cares about the sanctity of marriage. You'd think that the Son of Perdition and Jesuit plant Francis I would be handing out excommunication notices to Sotomayor, Roberts and Kennedy for this rather than worrying about the Sci-Fi threat of a global warming Armageddon, but alas, false prophets care only for false prophecy.