I have been on Nemesis Inferno a few times without shoes, it really does depend on the member of staff because although from my experiences most of the time they let you go on without but then a few people have said that I have to wear them.
If having to wear shoes is health and safety then why are you allowed if you are wearing flip flops or something similar to take them off (I know its because they could fall off but what difference does it make if you have sturdy shoes and take them off)?