From what I've been able to determine, the pre-boot sequence of the PS2 uses the laser "off-Phase" to determine from the colour surface whether or not this is a genuine disk and of what type (PS, PS2 CD, DVD). THEN it goes into the boot sequence that can be caught by the modchip. AR2/GS and the like would need to be produced using valid Sony OEM methods.

Valid PS2 disks are pressed not burned.

Hope that answers you.