SR7
Striker
Unless they used 316/L, then the likelihood is that any stainless fixings would sharp oxidise and be susceptible to pitting corrosion etc… coated/treat carbon would more than suffice. The design engineers would take all this into account, they wouldn’t choose anything based on a whim and the insurance companies wouldn’t sign the structure off otherwise. The structure will have to be compliant to a code.In the stadiums location I wouldn't be so confident that carbon steel fixings would be fine over a prolonged period of time