Perhaps the US and the ATP have different standards for recognizing which country you play for. I would bet that the USTA wants you to have a passport and some amount of residency before they start throwing money and whatever other benefits at you. Ryan Sweeting had dual citizenship if I remember correctly, and was attending a US university when the USTA convinced him to switch sides. I do wonder about this, though, but I'm not sure where to find the answer. I'll peruse the rulebook later on today if I think about it.
As for Jesse, he does have dual passports right? Perhaps he considers himself a Canadian born American, like John McEnroe (and my sister in law) are German born Americans.