I thought the same looking at his platoon stats the other day. When Robert and Eloy are back, Vs RHP: Vaughn LF, Eloy DH, Eaton RF (or another lefty OF as this could apply to next year). Vs LHP: Eloy LF, Vaughn RF, Mercedes DH.
If I recall, they thought he could catch. At least enough on a backup basis, maybe as a C/1B guy?
Or maybe they expect the DH to be universal after this year and thought they could survive a year with him playing a position.
As long as he is hitting the ball it's fine. Not many guys behind him I would switch him with anyway (until Vaughn starts hitting more consistently anyway).