VA benefits are not creditable coverage for delaying Original Medicare. However, these benefits are creditable for Medicare Part D. This is something that is very often miscommunicated to veterans.
Even if you have medical coverage under the VA, there are still many reasons to enroll in Medicare coverage to work with your VA benefits. Remember, your VA benefits only work at a VA facility. So, if you receive care outside of the VA health system, Medicare will help cover those costs.