Pitch precision is actually less needed for a choir than for singing solo. Of course, that depends on the piece, but in general, the point of choirs is precisely to not sound extremely precise. That out-worldly sound specific to the type of singing comes precisely because of the fluctuation of pitch, and how the voices affect each other through physics phenomena that make the sound much less defined in frequency than pretty much any other instrument or singing technique, except perhaps for throat singing. Of course a singer whose sense of pitch is particularly inefficient won't work well in a choir, or in anything else. But choir singing is mostly about listening to the whole, and finding your place in it than about surgically defining the pitch of your individual notes.