I've never heard of this. I do know that the Japanese were adverse to surrendering. Most would choose death over surrender. They were fanatics.
Once they surrendered it was considered a war crime to kill them.
Because of Pearl Harbor, the Bataan Death March, and a large dose of racism, Japanese prisoners (as well as hapless Korean and Chinese laborers) were routinely dispatched. I heard one old Marine from Guadalcanal say that rather than stay up at night to watch Japanese prisoners (and risk falling asleep on duty), they were simply shot. Japan was not a signatory of the Geneva Convention, either.