You are right.. ESC is commonly used to bail out of a game.
That is why you don't want a button dedicated to it or you (or a child) may accidentally hit it .
To avoid this most users use 'Shift functions' on their keyboard encoder
What encoder are you using? (I hope not a keyboard hack)
On my cocktail table I hold 'Player 1 button' then hit 'Player 2' button to 'ESCAPE'
EG default of the I-PAC:.
From the Ultimarc Website:
Holding "Start1" and pressing other buttons sends a range of codes for MAME functions such as "escape", "Coin 1", "tab", "enter". This means no extra buttons are needed on the cabinet. In programmable mode any input can be the shift key and all keys can be programmed with a shifted code.