Okay, here is definitive proof that playing games out does not make your team have more errors and passed balls.
I played the 1885 season, playing each game out in 1-pitch mode. I kept the Opening Day save from that year, so I went back and loaded it up and simmed out the season a week at a time.
Here are the fielding stats of the 2 seasons (The top season is the sim and the bottom is the one I played out):
And really, what would be the point of making playing games out a frustrating experience by making your team suck more than if you sim?
P.S. I won the League when I played the games out and finished a distant 2nd in the sim (mostly because my #1 pitcher got hurt).