The challenge of a "safe zone" encampment is the fact that once it is set up, the attraction of others (not in this state, but somehow able to get a one way ticket) to come here and pretty much know that there is free housing to be had. In order to make the safe zones effective, the state and the counties will need to overlay procedures and laws that discourage anyone from thinking that the safe zone is nothing more than a free hotel for anyone to come to Hawaii. As @inlanikai said: make their vagrancy the worst option for them instead. 
Than institute firm but compassionate policy that in-processes the individuals, links them up to services, provide a quasi-judicial ruling on the plan and get the person out processed in good time. 
Now the out-processing can include the wide gamut - mandatory medical help for the person to providing them travel resources to get them to places where they can be better served, whether it is here in Hawaii or on the mainland.