Depends on how far you’re bending it. Tight radius recurves I’ll use vegetable oil to keep the moisture from my steaming process from soaking in. Otherwise I don’t use any oil when bending wood. Especially with Osage, if the radius you’re bending is less than that of a steering wheel there’s no need to oil. Just Slowely apply heat with the heat gun. Keep applying gentle pressure and it’ll move when it’s ready. Forcing the wood to move before it’s hot enough throigh out is when it’ll crack.
Kyle