Big manufacturers are the reason for the myth about oil and there's a reason for it. They would rather YOU have to replace your dried out holster after 10-20yrs of use, than to have to replace them after a couple months because somebody got carried away with neatsfoot. The "NO OIL" policy is just to save them from the liability. Personally, as a small maker, I would rather depend on the prudence of my customers to follow instructions and only put a light coat of EVOO once a year. By the same token, if a holster gets returned that has been over-oiled or treated with Sno-Seal, they won't be getting a free replacement.
Like Red Cent said, this is a common discussion among small shop leathermakers. Some use Skidmore's, some use Lexol, some use neatsfoot or extra virgin olive oil. We ALL use something. Even John Bianchi himself immerses his rigs into warm neatsfoot before doing the final finish work. After leather has been tanned, repeatedly wetted, pounded, stamped and dyed, it needs its moisture replenished. Then it needs it periodically throughout its life. Contrary to popular belief, it does not soften holsters or cause the stitching to rot. All my work gets a good two or three coats of oil before I finish it and all leave the shop as stiff as they were after wet-forming.