Thats very tight
I would say its a definite NO to accept a 30min transfer in DOH, it is an efficient airport and transfer can be quite quick but the problem is the outgoing flights which in my frequent experience with QR can leave up to 20mins early, indeed on one occasion a colleague and myself we chased to board as the last remaining passengers nearly an hour before the published take off time. i would always go for at least an hour as it helps the blood pressure if nothing else. I do like QR though so recommend them.