Funny one this. I'm Type 1 diabetic on insulin. Pre-op I was suffering from insulin resistance and hyperinsulinemia. At first, post-op, I found myself dumping if I so much as sniffed sugar. Now the weight's completely off and my insulin requirements have droppped by about 90%, I don't dump. Pretty sure if I snarfed a box of chocs in 10 minutes I would, but that's not going to happen. Haven't decided if not dumping is neccessarily a good thing for me, as it served as a reminder to keep away from the sweet stuff or suffer the incredibly nasty consequences!
I don't know if the actual effects of dumping are harmful in the long run, but I do think given that dumping is completely evil, try and avoid it happening in the first place - and read ingredients carefully for those pesky hidden sugars!