Replacing Crystal Oscillator with DDS.
No.  In this case, it seems like the crystal is being used as a bandpass filter.  The idea is that the gain of the amplifier will be the largest in the passband of the crystal.  You cannot just replace it with a DDS as a DDS does not act like a filter, it acts like an oscillator.  You might be able to get away with a DDS for the transmit function only, but it's not going to work for the receiver.