I don't think it's a matter of fact that you can't dry wash over SS welds. It can be used for distortion control. The areas of consern are two (2)

1. Chromium depletion. It happens during the course of welding but is mitigated by the fact your adding filler. When you wash ( or what we use to call dry washing) over the weld without adding filler you are depleting chromium. It is easy to check, by using a PMI instrument to see if after washing your chromium content is still in compliance.

2. Heat input. Another item that can be checked in real time as long as you have known requirements.

Jim