I use those modules, with a 30A full wave bridge rectifier, to make up speed controllers for 180VDC treadmill motors. They work well, and I have yet to see a need to add any smoothing capacitors on the output, but it is still an option.
That sounds like a novel approach. The DC equivalent to a TRIAC is a SCR (Silicon Controlled Rectifier). It is like a diode you can switch on and off. I don't know if motors themselves care much about filtering. But lots like to be filtered from motor noise. One popular method of controlling DC motors is with H bridges. H bridge motor controller should put you onto them.