Your "posterchild against transracial adoptions" crack made me laugh! If we ever meet in the checkout line, I promise not to judge you for your DS's wacky 'fro, if you promise not to judge me for my DD's mullet from hell. I spent half of junior high school wishing for hair like DD's, but grew up to be glad that that wish wasn't granted. (I'm waiting for a curl to show up on her head, though, so I'll know what to do with it.)
Like BMJ, I've been trying to think of something to suggest, esp. re leave ins. For me, oil, oil, oil is the key.
As his hair gets longer, the ends are older, drier, more porous and fragile. That may be the cause of some of the new dryness that you're seeing. The chlorine/pondwater/sweat/sun combo from camp, and the picking out of the resulting mats would only make his hair more fragile, porous and dry. Is he rinsing his hair well after he gets out of the pool/pond? That would help.
I tell ya, though, my mind keeps coming back to the thought that his hair really needs to be braided (or twisted maybe?) if he's going to keep it on the longer side, considering all of his activities. I'm sorry, I know that your DS doesn't want to wear braids, so this is post isn't really helpful, and accordingly, it will self destruct in 60 seconds. While the clock is counting down, though, please forgive me for being blunt -- AA hair loose and free at camp ain't easy; heck, in my case it wasn't possible at all. Your DS may have to realize that keeping his longer hair healthy and presentable is going to require more effort (to keep the length) and/or compromise (by cutting it or braiding it).
Have more thoughts, but am too tired to force them into coherent sentences. Will post or pm later with them, if you'd like.