Well, I wouldn't expect a video game to reflect this, but you are dealing with a unique scenario here.
If you were to ask Joe Torre or Joe Girardi (or any of the players who have spent a lot of time on the Yanks since 1995) who the team's best defensive Centerfielder was, the answers would be a unanimous vote for Mariano Rivera.
It is well known in Yankee circles that he could have easily had a career as a Gold Glove Outfielder if he had not been such a solid pitching option (and if he had been able to develop into at least a mid-level hitter). Even at his ripe old age of 41 in 2011, watching him shag fly balls during batting practice was simply a marvel to see as he could do eye-popping things that no one else would even attempt, and always with such a sense of ease as if he was barely expending any effort.
As a relief pitcher he would never really get the credit for this next comment (in part because most people just don't get to see the evidence often enough), but Rivera is undoubtedly one of the best all around athletes in the history of Major League Baseball. He certainly has deserved multiple Gold Glove Awards for the Pitcher position during his career, but they haven't honored a reliever with that distinction in nearly 50 years.
Just consider that the guy has spent 22 years in the Yankees' system (minors, majors and post-season) -- appearing in 1241 games and throwing 1796 innings -- and during all of that he has yet to be charged with a total of ten errors.
He is the only active MLB Pitcher in the Top 10 on the All-Time list for Career Fielding Percentage at the position with a mark of .983 (thus ranking #1 in that category amongst current pitchers).
Only 15 MLB Pitchers have ever won multiple Gold Glove Awards, and more than half of them aren't even close to Rivera's fielding percentage. Jim Kaat won the award 16 times yet his career fielding percentage of .947 ranks just 240th in history. Bob Gibson won it 9 times with a mark of .949 (230th all-time). Mark Langston won it 7 times at only .941. The only two multiple Gold Glove winning pitchers who really measure up are Ron Guidry (5 awards, .981 pct, would rank 17th all-time but fails to qualify due to under 500 games as a fielder) and Mike Mussina (7 awards, .980 pct, 17th all-time); sort of odd that both happened to spend significant time with the same franchise where Rivera has been from day one. Greg Maddux holds the record with a pretty amazing and ridiculous 18 Gold Glove Awards during his 23-year career, but while his overall fielding percentage of .970 is solid, it's still just 68th on the all-time list.
It's pretty amazing stuff when you consider how good Rivera is at all of the elements of pitching
aside from fielding. Even still, with all of the above being said, I don't think the computer mind of a video game should be putting Mariano in to play the outfield unless the team has run out of position players capable of handling the spot. Despite the fact that it makes some logical sense, it's simply not realistic; it's not as if Showalter, Torre or Girardi have used him that way even though I'm sure there were many times when they wanted to.