I don't have much experience with this, but based on research and reading I've done, I would say no. If a program wanted to accept someone without funding, they would accept them without funding instead of rejecting them. The one caveat might be if the rejection letter explicitly states that the only reason for rejection is lack of funding. Even in that case, though, I would advise against it as it feels like it would be whiny/in bad form to try to negotiate. And aside from that, aren't unfunded PhD programs generally a bad idea?