This isn't a new thing - it has always been the law. Some campgrounds have strictly enforced the rules concerning minimum wage and taxes, but some private campgrounds have skated around them, either ignoring or claiming exemptions that may or may not apply. As Wendy explained, the value of the campsite is taxable, but it is also tax deductible in many situations.
If you work 9-6 in the campground store or office, it is pretty tough to claim that you are "required" to live in the campground to do the job, but many campgrounds have used that exception to justify excluding it from taxable income. It probably wouldn't hold up in an audit, though. But if any nighttime security or after normal business hours responsibilities were part of the job, it would probably be ok.
The individual workamper might be asked to provide the IRS with an official statement from the employer that they were "required to live in the campground". A cautious worker would ask for one up front rather than trying to get it when the IRS audit happens 6-18 months later. Obviously, the taxable nature of the site has a significant impact on the workamper's income, so best to know up front. But the IRS could still deny the employers claim that you were required to live onsite, so even having the written statement is not 100% foolproof.
I think the new healthcare provisions going into effect are causing a much closer look at a lot of small businesses that in the past may have skated around some regulations. There are requirements to provide health insurance for a lot of people who may not have been covered before, and this leads to formal scrutiny by several gov't agencies.