Hi,
1) A stock ME7.5 can be read over OBD, but yours is not stock! Because your new ECU has "software" (aftermarket tune) installed, you will have more trouble than it is worth trying to mess with it. If you want to reuse the HW you will need to uninstall the software. To do this you will need to open up the ECU and see if it has a riser card in it. If it does
not have an extra card inside, you can probably reprogram it to stock BIN in boot/bench mode and start from there. If it
does have an extra card inside, you will need to remove the riser card, install a normal flash chip and reflash with a stock file. My guess is that you have a riser card and this is probably why the read is scrambled, although with that clone HW in the mix too you have added a lot of different variables. Because your new ECU has "software" on it it is
not safe to read/write it over OBD.
2) The IMMO is in both places, but it is easiest to turn it off in the "little" one (EEPROM). The "big" chip is called Flash, it has the software operating system which runs your ECU on it. So, the actual programming code that checks the IMMO is here in Flash, and it is possible to bypass IMMO by replacing the software on the "big chip" with software without IMMO. The "little" chip is called EEPROM, and it has the car specific variables on it like VIN, IMMO configuration, trouble codes, adaptations, workshop logs, variant coding.
It is easiest to disable IMMO on most ME7.1/7.5 by editing the "little" chip using
http://nefariousmotorsports.com/forum/index.php?topic=6134.0 and
http://nefariousmotorsports.com/forum/index.php?topic=1168.0title= .
3) See 1. You will need to uninstall the aftermarket software which might require removing a riser board or might just be boot mode.