Can't even do that in Texas anymore, not on a commercial basis. Hawaii may be the last state where you can, and I'm sure they have strict rules about doing it. Between Health Department rules and Air Resources Board rules, just doing real barbecue of any kind in L.A. County is not easy.
re: Will Owen
Yep, in the ground is going to be impossible with health regulations. I think there are a few caterers however that would bring Hawaiian food to you if you pick a location. Or, you might be able to hire a crew that will supply and dig whatever you need. However, final cooking/serving will be up to you which will be risky if it's an official work function.
As Will stated even Hawaii is tough. A hotel where I've been for years used to do it in ground, but stopped 5-10 years ago and now dig and cook an 'empty' fragrant pit and serve a pig cooked elsewhere.