Sure, it is meant to indicate that any marriage that has "God" in it as the foundation of the couple's life will be successful.
Is it? The context gives no indication that the scripture is talking about marriage at all. It seems to be talking mostly about cooperation and building relationships (though not specifically marriage) that make your life meaningful. There's also no indication that the third cord of the threefold cord is meant to indicate god. The context is entirely about people helping one another so there's no reason to believe that the third cord would be anything other than another person. Actually, there's really nothing to indicate any intrinsic significance to the use of the number three for the cords - a twisted rope made of two strands doesn't stay together as well as a braided rope of three, so it may simply be a relic of the fact that a threefold cord would be much more common and the author was just pointing out that there's strength in numbers, which, again, is supported by the context.