A rental will only cost you about 35 bucks from wetsuitrentals.com. I haven't heard any stories about White Lake being too warm for a wetsuit. 1.2 miles is a long way to swim in a surfer wetsuit, i'd say rent one because you'll most likely be using it. If the water's as warm as Pinehurst was last year, even if it's wetsuit legal, I doubt I'll be wearing mine.
White Lake is spring fed and is pretty cold, but it can depend on the weather, too. The lake is shallow and clear, so it heats up some if the weather is pretty. Someone yesterday said something about 60 degrees last year? I'm doing the sprint and do not plan to wear a wetsuit.
I did white lake half last year and as far as I can remember everyone was wearing a wetsuit. If it is wetsuit legal, which I think it always is, I would wear a wetsuit. I rented one for the weekend and was glad I did. It's a long day so might as well get the extra benefit.