Jerry,
I have no problem with harmony lines occasionally sharing notes or counter-melodies crossing over each other.

I grew up singing in church, both in the choir and in the congregation, and it's not at all uncommon for the altos and tenors, or for all 4 parts occasionally to share a note. Plus, I'm partial to countermelodies, as opposed to harmonies that consistently stay above or below the melody. Countermelodies often do hit the same note as the main melody in a few places.

Where's the harm?

In fact, maybe one reason I'm not wild about barbershop is the overemphasis on always having 4 distinct scale notes on each word of the song. Paradoxically, I think having the various parts sometimes hit 4 different points of the scale, sometimes split onto 2 separate notes, and sometimes all sing in unison ADDS variety and complexity to the presentation beyond the usual "barbershop" 4-part harmony.