It seems to me like anyone doing small business HR consulting would need to also know about the field they're consulting for. How are you supposed to help develop and employee handbook for an insurance company, for example, if you don't know a thing about insurance and the different jobs there are in the field? I don't think you could do it!
I wonder if there are HR consulting firms out there that specialize in specific industries? If so, I think I would hire a firm like that rather than just a general HR consulting company.