If he had polio that only affects your motor neurons. It doesn’t affect your sensory and involuntary muscle function. Lucy apparently had no problem with her muscles or movement. That’s why he was hanging out with her for years!
If you ever go to one of FDR’s retreats and take a tour you can ask the docent where Lucy’s room was. LOL The response is usually, “We are not allowed to mention that.”
Many years ago, touring the little White House at Warm Springs, the tour guide didn’t try to hide anything.