by imprints do you mean the smaller companies that DC has absorbed, like All-American? it gets a bit complicated in that DC bought out certain characters and titles from companies like Quality and Prize, but didn't purchase the companies themselves, and published the purchased titles/characters under the DC label.
There's strong corporate ties to smaller companies like ACG, but that has more to do with the distribution company Independent News which was owned by the same people, but was run as a totally separate company. Independent News invested in several other comic publishers in order to ensure a steady flow of product in their pipeline, but DC was the only one that they owned outright, I believe.
Marvel is a different situation, as Martin Goodman used so many different corporate names. I believe that the Overstreet Guide has a pretty good list of all those corporate entities, up to the 60s at least.