Will a ECU without immobilizer work in a car with an immobilizer?

I have a Euro or UK spec My02 WRX with the AF531 ECU. I would want to have the ECU reflashed by an ECUTEK dealer but the problem is I live in Asia.

I was thinking of buying a used ECU from a US spec car in the US and have it flashed in one of the many ECUTEK dealers there and use it in my car. Finding a used ECU in the states seems to be so much easier.