How much Structural Reinforcing Steel is required in the first three feet of decking to satisfy the bonding reqirerment befor you have to go to the Alternate Means. as listed in #3
Its not specifically stated in 680.26 (C) (3) to answer your question, #3 comes into play if the structual steel is the incapsulated non-corrssive style or reinforcing steel.
If the steel in the deck conforms to the requirements of the building code such as section 1903.5 of the IBC and complies with the ACI 318, it should be suitable to be used as the equipotential grid.
Remember that 680.26 doesn't mandate or require steel to be in the deck. It only requires the steel, if present, to be bonded as a part of the grid. The requirements for the deck steel is mandated by the building codes.