"dominant trait " in diploid breeding is easily defined and understood. In Octoploid breeding, "dominant" is a word many people use to indicate that a seedling flower displays a trait(or traits) more so from one of the parents. In diploid breeding it is the one actual gene for a trait they are talking about. In actuality, there probably are diploid type dominant genes in dahlias but we have no easy way to identify them. Meanwhile, people like to use the word "dominant" and I used to cringe when I heard it but now I am getting used to it as you do need a word to say that one parent seem to transfer more of one or more traits to the seedlings.
Knowing how genetics works can be useful but it is "only nice to know" if you cannot apply the knowledge to actual dahlia breeding. Octoploid breeding is the same type of breeding people used to do before they knew about genes and all that. If you were breeding wheat you selected kernels from the best plants and eventually you would have a new and improved wheat variety. 
Hollyhill Red Spider in 2009.
