Odds Nikaidou-mama walks on them?
Since Nikaidou specifically mentioned locking the door in 124, I'd say very low...
HOWEVER!
The odds that Nikaidou's maids HEARD them...
I can already picture it:
The girls come out of the room for dinner, all steamy and flushed, the maids are trying their darndest to not have anything show that they prob. had the walls in the whole mansion vibrating, only for Nikaidou-mama to drop a line ala "So how was it? wink wink nudge nudge" over the pot roast.