With an USL it's not a good idea to fly over a built up area in case of an inadvertent release or an unstable load that requires pickling off - but do remember that the pilot will always have a far better viewpoint than any ground observer could.
Engine failure isn''t the major consideration in the cruise for a twin as the other engine one will allow the aircraft to be manoeuvred safely away from the mandatory infants school and packed old folks' home before jettisoning the load over a safe area. We used to teach pilots to prioritise dropping it on MOD property if possible.