I’ve never heard that about J.E.B. Stuart. It would make more sense than Lee inexplicably sending his men up that grade/hill to die. Lee wasn’t known for sending men into a meat grinder. If so, it sounds like it was an intelligence issue, not knowing where Custer’s (7th Cav?) were.
I wish I could remember the name of the book. It was really interesting and was pretty well supported by accounts from Confederate officers other than Lee. There was documentary evidence to support the idea that Stuart was a part of the attack that failed.