DNA is not exact, but at least for the main parts, it is. Sally asked why does it matter... but it can help so you are aware of common health/genetic issues.
As for conjoined toes, lots of dogs have them, but if a breed standard for any, I can't find it. I found a gazillion forums (okay not a gazillion but lots, including retrievers, shelties, labs, etc) with people showing their dogs' feet and asking others. Most breed boards said happens, not common.
I noticed a lot of the dogs with joined have hare-feet (elongated middle toes), but the basenji standard calls for
" Feet-Small, oval and compact with thick pads and well arched toes. Dewclaws are usually removed"
Breeds with hare feet include several of the toy breeds, Samoyed, Bedlington Terrier, Skye Terrier, Borzoi, and Greyhound.<<