Couder's experiment still depends on the wave train leading the particle. You might consider this to be valid where the particle speed in less than c, as you could indeed propagate a pilot wave ahead of it. But by how much?

Couder's particle is constrained to move at the wave phase velocity, but the direction of movement after diffraction is a function of group velocity. So, applying Couder's model to your concept of (compression? transverse? you choose!) waves in dark matter, please calculate the diffraction pattern of 1 keV electrons, 1 MeV electrons, and 2 eV photons through the same double slit, and compare with experiment. And you might also ask how neutron and proton diffraction will compare. It would be interesting indeed if all particles, regardless of mass or charge, had exactly the same interaction with dark matter.