I used to degrease osage religiously. I stopped one day when I read a Dean Torges statement that he thought freshly cut osage didn't need to be degreased. I have found this to be true, at least if you use Urac-185 for glue as I do.
To date I have spliced about 50 pairs of billets into bow staves without degreasing, always added a piece to the back of the handle to give me more to work with and never had a failure. All the splices were freshly cut.
I have made 20 or more BBOs with no degresing of the osage core or bamboo backing, no failures.
I have never oiled a piece of wood to heat bend it either and don't remember the last osage stave I worked that didn't need some heat gun correction, all of mine do, no exceptions.
Lots of old wives tales out there about what you have to do to when making a wood bow.