Should I use a steel leader in case a shark bites?

What kind of rod setup are you using? If you are using your normal light tackle like your bass rod, then I'd stick with a 40-50# mono leader at most. That should hold up for most of the toothy critters you'll encounter including smaller sharks. Anything that breaks through that big of a leader you probably don't want to try to fight with light tackle anyway.

If you've got a dedicated surf/offshore setup that can handle really big fish then you may take a different approach.

I've got a mix. My smallest pole has 30lbs braid on it which I'll use for tossing lures for smaller game. My other 4 poles are my bigger setups that I mostly use for big cats. 50lbs braid or higher. One of those is a my big shark setup which I will for sure have a steel leader on.

From what I've been reading about fishing for bull reds, seems like sharks would be mixed in quite often.

Light weight tackle nah, but medium to heavy there is no reason not to use steel leader.