Yes, if you are the parent receiving the payments, unless the child support payments were specifically designated for medical. That money is considered your money to spend as you see fit. No, if you are the one paying the child support. Payments designated as child support are never deductible.
Yes, but your question is academic.The term "medical dependent does not apply to divorced and separated parents. A special rule allows either parent to claim medical expenses, they pay for their child, regardless of whether they are claiming the child as a dependent. Again, child support received is generally considered your money to spend as you see fit.