This is nbody simulation, I think that its already implemented in terms of just simulating Newtonian physics.
The effect is rather small, so it would require a long time to show any visible difference. Additionally, we deal with finite math here, so rounding and truncation errors over this large a time frame (many steps) may actually wash out the resonance effects.
This is why Eric added a calculation of the _resulting_ effects on ring systems by local moons... essentially bypassing the step by step development and jumping directly to an end result.
So, yes, nbody simulation does by itself contain resonance effects, but for a concrete implementation, there are issues, which makes it dificult for a fast sandbox experience.