If hop stands led to significant amounts of DMS, then I would expect it to be an issue regardless of whether you covered your kettle. Since your wort isn't boiling, there's nothing going on that would really drive off the DMS even if you left your lid off.
I did a lid-on hop stand on my recent Bo Pils starting at 180F for an hour. Didn't notice any DMS at all in the finished beer, FWIW.