I thought that anything not in a rate equation was automatically zeroth order and therefore did not affect the reaction. However, I have heard that catalysts can be involved in a reaction while not being in a rate equation. How can this be possible?
Enzyme kinetics is one area of catalysis that has been studied extensively. The Michaelis-Menton equation being one of the central pillars and explicitly states the roles of concentration for both the substrate and enzymes.
Also, to answer your question: the rate equation is at times more interested in establishing equilibrium conditions than obtaining the time it takes to get there. The time to reach equilibrium is slightly neglected as the question "are we there yet" seems trivial when distance = rate times time.