Understanding that the relationship between you/your business and those that provide labor and services is not simply a by-product of how you compensate them is the first step in making sure your real estate (and any other business) is protected appropriately from WC (and GL) exposures. Securing and confirming coverages is a must when dealing with any and all contractors and service providers.
Unfortunately, in today's litigious world, the risk of using uninsured “spot labor” far outweighs any short-term time or financial benefit. If you are currently using and satisfied with such labor, review with your legal and accounting advisors and consider securing coverage for them, in the most appropriate and efficient manner they/you decide. It only takes one uninsured claim to put you out -of-business.