We do not test any standard component for X-ray emissions.. within aerospace applications there are two DACs that probably may suit you, AD768S and AD9731s...
in general, the X-ray is nothing else that ionizing radiation that could corrupt the data in an internal registers, making the part misbehave.
If you protect the systems with a metal case or similar, you should not expect any problem...
If this is not the case, probably you must refresh the registers often to guarantee that the part behaves correctly, and reset the system in case an error is detected.
