Yes, you are right. It seems that Ibis hotels (at least in Poland) do not have "expedia special rates", so you can not redeem vouchers on them. But proper Orbis Hotels (i.e. hotels with the name "Orbis") are anyway better than Ibis and they are marketed just below Novotel. Plus, you can find them in all Polish cities where Ibis is present and far beyond. The only exception is Warsaw, where you still can go for Novotel (I would recommend Centrum) or Mercure for less than 10 pounds.