Do NOT put current through a bearing. The lubrication and intermittent metal-to-metal contact produces the equivalent of electrodynamic machining, which removes metal from the bearing surfaces and suspends it as metal dust in the lubricant, rapidly destroying the bearing.
(This effect was discovered when a Russian engineer tried to cool the points on a gasoline engine ignition system by immersing them in oil - and found the points, instead of being protected, were eroded to nothing within a week.)
If you're going to use the mast as a conductor you'll need to provide a brush and slip ring, and insulate the bearing on one side. (At that point you might as well use TWO slip rings and skip using the mast as a conductor, with all the other problems that might cause, such as rapid electrolytic corrosion at the joints once they get wet and ordinary corrosion makes them resistive.)