I wonder if someone got confused and mixed up Mr. Rogers with Bob Keeshan Captain Kangaroo. He was in the Marines in WWII.
You are correct that Bob Keeshan was a Marine and that there are lots of rumors out there.
Besides the Mr. Rogers rumor, there is a rumor about Lee Marvin and Bob Keeshan at Iwo Jima receiving the Navy Cross.
We know Rogers never served.
As for the other two, the truth is both Marvin and Keeshan were Marines. Neither were at Iwo Jima. Neither received the Navy Cross.
From what I've found, Captain Kangaroo signed up too late to see action and Marvin was in the Pacific, hurt in Saipan and received the Purple Heart.
Of course without further research even I could be wrong.
:-)