No need to worry, Bass and Synth Bass mode do not do any rolloff on the signal.  The main purpose of these modes is to allow any pitchshifters to track lower notes.  The expense of this is possilbe slower tracking, but it will also probably track small simple chords better (octave, P5, and P4 combos for diatonic algs, possibly other chords for chromatic algs).   The other thing Bass modes do is condition algorithm tone shaping filters to sound better for Bass instruments.  Off the top of my head, I think this affects tone shaping filters in Sculpt, EQ Compressor, MicroPitch, and CrushStation.