Per Baseball Savant, Odor would have hit 17 homers if he’d played all his games at Yankee Stadium, and 17 if he’d played all his games at OPACY. He’s basically gaining nothing by moving from NY to Baltimore. Any statistical improvement is going to have to come from actual improvement, not switching stadiums.
You have to be on a 40 man roster to join the Union. I'm not sure if you stay in the Union if you get removed from the 40 man roster.
No way the MLBPA is going to put all the minor leaguers in their Union.