If I made a linux build from unity it will work on the arm processor ??
What do you mean by primary approach? If I want to run Android games on RPi, I need to use Android, right?
I would also think there are more games for Android suitable for this specific hardware caps than on Linux.
RPi is not made for running Android. If you want Android, buy a smartphone or a tablet, it will be much easier for you. There may be some ROM which runs on it but I guess it won't be smooth. RPi is aimed at regular ARM distros. And there are some, like the Raspbian, which are specially optimized for RPi.