I've never heard of this in a UH-1 manual before - not that I'm that experienced in the UH-1. I suspect it is in there because of an accident where someone thought this may have been a contributing factor.
Probably more correctly stated, it may have been if you are rolling left and have an engine failure - a steady bank angle shouldn't make that much difference unless you delay your reactions a long time.
UH-1 experts???? Over to you.