That is how it is done; you'll have to switch to the neph at the clinic you are dialyzing at. You can ask your present neph to apply for admitting privileges at the unit closer to your home - admitting privileges are easy to get for an MD - and then he can cover you at the new unit- unless he is unwilling to travel that far.
Everyone's situation is different depending on what insurance coverage they have, where they live, and other factors. In my case I'm covered by an HMO but dialysis services are contracted out to private dialysis units. I had my HMO nephrologist, 3 staff nephs at the dialysis unit, and a transplant neph at UCLA. Nephs everywhere, nephs coming out of every ear, a neph a day...you get the picture. In your case it sounds like the dialysis unit you want to use has an arrangement with the nephrologist they want to send you to. If push came to shove I'm sure you would get your way if you wanted someone else.
And they seem insulted when I make them pull my chart and read the Dr.s orders.