I had mine done a while back, and they told me the same thing.... removing the whole gland would cause a concave nipple. I wanted them to remove the whole thing, but they wouldn't. Kaiser was paying for it, so I had no say. A tiny hard lump returned within weeks to both sides, without being on any hormones.
It's not bad, but I'd still like the entire gland removed. I have heard some surgeons will place a tiny implant beneath the nipple to keep it from going concave.