No way, would ANY shop or maker ,polish BOTH brass and steel 'together'on the same wheel, the brass would contaminate the wheels and booger the blue job of ANY salt solution, causing 'spots' in the metals finish, that is VERBOTEN around the gun shops and service departments of the factories we ever trained at..................if one "sees" polishing marks , it is from "after the fact" buffing in any particular gun and using a 'harsher' abrasive than really needed ( like wiping down a gun with ones 'flannel' shirt sleeve or an old burlap potato sack......) or as many do today, using a 3M Scotch Brite pad, on a "finished" gun..........
as for the pin holes, "casting craters" ( very miniscule though they be) are quite common in brass, bronze "gun" castings...same went for stainless casting, yes even done by Ruger, ,I refer back to the early Old Armies, in 'stainless' and if one ever tried to polish one out, you can and will "open" other voids or pin holes, file/sand ONE, and open two or three....again, we ran into this often in refinishing firearms............saw 3 'brass frames' on and off guns today at the show, and they had 'casting' pin holes and many shrink "cracks" inside the grip frames...nature of the beast. Bill Ruger had just cause and GOOD reasons to get the 'brass frames' out of his shops.