I'm going to link a few things about MAME documentation the 1st explains having monitor orientation .ini files they will be called VERTICAL.ini and HORIZONT.ini (I believe the caps are necessary),
The 2nd talks about commandlines and rotation but you wouldn't need to use a commandline you would want to set you rotation monitor in your VERTICAL.ini You would set rotate right or left (ror or rol) which everone you need to 1 instead of 0 then all of your vertical games would rotate.