last first: Most impeller machines had relatively short wash cycles so there might not be time for the enzymes to do much.
Soil Separators: In many Hotpoint machines, there is a little removable perforated guard ring around the impeller that has small holes near the bottom and larger ones above, or maybe just the opposite. During the washing and rinsing operations, the water level in the sump is at the level of the fine holes of the ring, in theory, and prevented food soil from recirculating. When the motor stopped for drain, the water level rose and the heavier, larger food bits could flow through the larger holes where the drain action could have a chance to carry them away. You also had to remove it once in a while and scrub it. A Kelvinator built in (D&M) we have has a similar primitive filter around the impeller. The GEs with the bow tie impeller had a couple of good things for dealing with food soil. Screwed into the sump at the 12 o'clock position of these machines, is a stainelss steel "L" shaped piece of metal that tapers down a bit near the bottom of the sump. When the dishwasher motor reverses to drain, the impeller runs backward. It does not throw water, but it really swirls the water in the sump. The metal strip acts to control the swirl and force food in the draining water down into the drain. Before each drain ends, there is a brief flush to help further clean out any remaining particles.
I guess none of you have seen a James or Ling-Temco in action. They had glass doors/lids and really had a water movement pattern with pretty good filtration.