You can have ditch cut in the cam journal. It affects Rod bearing oiling zero. Has zero affect. Besides, no matter how you do it, the oil going to the rockers is self limiting, even with a grooved journal. As RPM goes up, the time for oil flow goes down. It also limits because oil flow is controlled by the leakage at the rocker and oil feed to the cup and adjuster.
It's all about oil timing at the crank. Nothing else.