I have Mala set up with DaOldMan's rotation plugin.
I'm using the method from SGT's "multiple emus in one list" stickied thread to put all the arcade games in the MAME gamelist regardless of emulator.
The rotation data comes from mame.xml, including games I added which don't run on MAME.
The result is automatic rotation for everything.
Mala keeps track of which way the monitor is turned and displays the appropriate horizontal or vertical layout.
It all works exactly the way I want.
However Mala is not being developed to keep up with the changes in MAME, so it's a PITA to use with newer versions of MAME (v.162 or thereabouts IIRC).
If you're using a newer version of MAME and plan to update it in the future, you might as well start out learning how to use a front end like GameEX which is being actively updated.
Just a heads up: Have the monitor rotate counter-clockwise from horizontal to vertical.
The majority of arcade games work that way, including Sega NAOMI and Taito Type X.
The ones that are opposite are run in MAME where it is easily corrected.