Those are perfectly legitimate questions.
Are there dwarf races of redfoot tortoises? Well, not really but sort of. Many of the redheaded redfoots that have been exported from Southern and or Eastern Brazil (Bahia State) do have males that are sexually dimorphic at a relatively small size...like 6 inches or so. They are clearly sexually active and quite capable of breeding as small as 7 inches and probably even less. Many of these individuals that are imported also show signs of being fairly old or mature with smoothly worn shells. BUT, I haven't had a female, nor have I heard of a female that has laid fertile eggs when smaller than 9 1/2 inches and they grow to be a good bit larger. For instance, one female I have now is over 12 inches and growing fast and one I got back in 1984 (from the famous Pet Farm "dwarf redfoot shipment" allegedly from Paraguay but actually exported from Argentina and composed of Brazilian tortoises) grew to be over 13 inches.
In all likelihood they are similar to Key deer and rosy rat snakes from the Florida Keys which are smaller than their mainland counterparts in the wild but that will grow to be 'normal' size with a rich captive diet. So probably, there is a limiting factor where they are from that contributes to their being somewhat smaller than other redfoots.
Marbled cherryheads are simply individuals of the redheaded race that have large amounts of white in their carapace. In my experience most of this white color, though very beautiful, turns either black or at least a darker brown once the tortoise reaches adulthood and is kept with access to full sunlight. Some though seem to maintain a degree of this white color.
Lastly, there are 'giant' redfoots. These are the very large animals found in Paraguay and neighboring Bolivia.
None of these obviously different races have been formally described though.