Banded killifish are great but they do not provide a big meal for your bigger SMB. GSH can become a problem apparently but if you have YP and SMB to prey on them you should be fine.
I stocked BKF and spotfins in my pond, I think they have established but I am not sure as I have not seigned and they don't get suckered into the fish traps. Spotfin shiners are crevice spawners so to help ensure they establish you should create the proper spawning structure. I made structures out of blank cd's and washers that I hung from my dock, I have seen the spotfins hanging out here and I have seen eggs on the cd's:
Even a big spotfin can be eaten by a 12" SMB. A big 9-12" GSH is only vulnerable to a REALLY big smallmouth so they stand a better chance of creating a sustainable population.
