Have use various rack-mounted units in the past, but there is no real difference between pedals and rack units.

The most important thing is that the Output Chord in BB must send on the same channel as your unit, in order for it to receive the chord information.

Then most units only work more or less correctly if you use chord symbols that represent 3 or 4-note chords. In other words; C7#5 is ok, but C9 is not OK etc.

In spite of the fact that both BB and most vocal harmony units claim they follow the international MIDI protocol, not all chords are represented correctly. I have taken this up with both PG-music and TC Helicon, but to no avail.
So sometimes small mistakes can happen, like e.g. C6 been seen as Am7 or Cmaj7 as Em7.

I hope this helps.
Brgds,
Tonnie