I thought that happened with fall arrest harnesses as the leg straps cut off the blood supply through your inner thigh. It's not so much the suspension, but where the straps cross.
No,that's not true. The femoral vein is too deep to be cut off. The position of the leg straps is relevant because proper leg straps allow you to hang in a sitting position.
Huh. I suppose thinking back the guy that told me that generally didn't know what he was talking about. I never bothered to double check. I don't do anything that I need a fall arrest system anymore, but maybe I should do some reading.