You can add rubble and it will colonize similar to how the ceramic rings used in fw work. However, it should have some finer mechanical filtration before it or it will turn into a nasty sludge pile that doesn't do much for filtration and blocks flow, and it will be difficult to clean. If there's not a lot of space in the filter then it might be better to save it for possibly running something like phosphate remover (assuming you don't have a skimmer - if you do then you probably don't need that). If there is space, have the water flow through filter pads first and change them regularly.
For a point of comparison, a long time ago I had a big canister filter on a 55gal (which also had a bunch of live rock in the main tank), and I had a stage for prefilter pads then phosphate remover and then rubble, which ended up colonizing not just with bacteria but also beneficial sponges. Worked really well but it was pretty roomy inside.