As long as it has been washed, screened, and re-graphited, it should be fine.
I use reclaimed shot (7.5-9) in most of my 12 ga, .44 Mag, and .444 Marlin loads. (And I will use it in 20 ga, when I start reloading for it.)
The rifled barrels of the .44 Mag and .444 Marlins obviously throw their own wrench into things; but the 12 ga loads pattern just as well as low end 'target' loads. With some wad experimentation, I could probably improve patterning, but I don't really care. The patterns are good enough to for small game hunting and breaking clays, and that's all that I care about.
The shot that I use has a small amount of steel mixed in (maybe 8-12 pellets per 15 lb), but it's easily removed with a magnet. Any pebbles that managed to hang around in the mix are easily removed by pouring the shot into a shallow pan and giving it a quick once-over.
Even so, those contaminants are a non-issue if you're using a shot cup (or standard wad). Pebbles and steel shot will only cause a problem if it contacts the bore, such as in loads using fiber wads, nitro cards, or cork wads in place of shot cup style wads.
Most of the pellets in what I use have notable dents and deformities. It isn't substantial, in that they're flattened or have grown three heads; but there are noticeable dents from the shot charge getting compressed when it was fired the first time.
And, just as a note...
I'm not running this through $250 Mossbergs. I run those loads through 2 heirloom Winchester 12 ga shotguns.
With a plastic shot cup, contaminants won't hurt the barrel.