There are a lot of things that make Wakka look like he's from Hawaii. Well, he's asian looking, and 80%-90%(though probably more) of Hawaii is made up of asians who do look kinda like Wakka. In fact I know of at least three guys who really really look a lot like Wakka.
It's hard to explain. The Asians you're thinking of probably are really white, really slanty eyed dorky looking thin FOBs. Hawaii asians are completely different. I guess like Lilo and Stitch, they look asian, but are definitely darker and look more "local."
Wakka has a pretty nice tan going on, and he also has dyed hair which is common here. In fact it seems like it's a necessity for every asian guy in hawaii to dye their hair.
Wakka seems to look like the kind of guy local asian guys here try to look like. Not the spikey tall hair though. Even if they wanted that hair I doubt anyone could duplicate it. I mean, his body type(buff)and kinda rough looks. The clothes maybe are similar. Local guys like to wear lots of tank tops and board shorts, which if you interpret Wakka's clothes, are somewhat similar. But maybe that's stretching it.
It's still hard to explain. All I can say is that if you came to Hawaii, you'd see that the bulk of local guys here do have striking resemblances to Wakka. It does seem to me they modeled Wakka from local sources in Hawaii.