I actually opened the thread to do just that, and saw your post. However, a correction: all three dayanim were in the room, but only one saw her submerge her head.
http://www.hebrewbooks.org/pdfpager.aspx?req=920&st=&pgnum=359&hilite=
He is only mattir, as you point out, b’dieved, and only when the dayanim were in the room.
Rabbi Avraham Gordimer wrote an article excoriating Rabbi Fox for his teshuvah on a number of levels. The one point I don’t agree with him on is his limiting the heter to where one dayan actually saw. The case was in fact that way, but R’ Moshe’s reasoning wouldn’t seem to require it.