But as for as the bottom line of what is allowed under the law and what isn't we each need to check the statutes in our states to know for sure what the rule applying to us is.
In my case, I have asked this same question of lawyers and judges since day one because until my x remarried it was a HUGE problem. X would go months w/out ever seeing ds, his family would take his time, and they would tell ds things like 'mommy wont let you spend time with daddy'.
It was nuts so I've asked every attorney for myself, for x, and the judges we've been before clarify it for me. They have all said that the laws in MT apply it this way:
When the parenting plan gives a parent "Visitation" it is not delegable and that parent must use it or lose it. But if that parent has "joint parenting time" in the parenting plan, they can delegate it to another adult so long as ROFR and/or flexibility provisions aren't present.
In the case of VAStepmom, if her situation were in MT and if her dh had visitatiation time by court order, it wouldnt be the cp in contempt as she had originally asked, but it would be her dh.
I encourage everyone to check your own states statutes and be aware of how the courts will address the situation in your state as opposed to what "should" be done.