Should I be concerned about deep fryers with Prop 65? Nearly every model has this, even ones made specifically for restaurants.

Prop 65 is a warning about a long long list of chemicals which could or are present in even low to very low concentrations. You can read up on it and see the list online if you want. If I were making something involving food, I would put a prop 65 warning on it on general principles.
If the question gives you a headache or heart disease, better not take aspirin. It's on the list.... :-)