Can someone in hiding adjacent to a Minyan be considered to be davening bi'tzibbur - v4 #4 by R' Aaron Cohen

The Jews in the Kovno Ghetto constructed a Bais Medrash for Tefilla and Torah, and they made a secret room adjacent to it for those hiding from the Nazis. The question arose: if they could hear the Tefillos from that secret room but could not see the Bais Medrash, was it considered Tefilla Bi’tzibbur?

Reference Material (pdf)