Given that this law has been in place since 2001, I'm more than puzzled by the fact that the startup world hasn't been shaken by it: I feel I have to be missing something. After all, I understand that startup hubs like the bay area offer irreproducible benefits, but I can't believe that these incentives haven't made Hawaii the center of activity for at least some subset of startups -- capital-intensive seed-level startups, say. And that's not even considering the other perks of Hawaii ;)
Well, I guess isolation is much higher barrier after all. Many says it is difficult to find people---for senior staff you are more likely to relocate them from mainland, but people are reluctant either if they have family, or if they think it isn't as easy to find other jobs here as other tech hubs in case if your startup tanks (plus the living cost is high here). For junior staff the only source is UH and some community colleges; there are talented people, but the pool is inherently small.
However, I do know some local startup benefitted by Act 221, hiring local people and doing good. It's just that the law itself isn't a silver bullet.