Do I need insurance for a truck I only use on my own land?
Not by law, generally, since registration and compulsory insurance attach to public roads. You still have an exposure: if it injures somebody, a claim follows, and a motor vehicle exclusion on your homeowners policy may leave it uncovered. It is worth checking rather than assuming.
Does my homeowners policy cover the utility vehicle?
Sometimes, under a carve-out for equipment used to service the premises, and sometimes not. It is a wording question that varies between forms rather than something you can reason out. Send us the policy and we will read it.
What if the ranch truck is damaged or stolen?
Usually nothing covers it by default. Physical damage on an unregistered vehicle needs scheduling on a farm policy or a specific endorsement. If it is worth real money, it is worth naming rather than assuming.