The Dark Brotherhood itself is already confirmed to be ingame. The only guild to be, in fact. Don't ask for a quote, but I believe I read it. Other people could back me up I guess.
Regarding the Black Hand... well, I am no DB lore expert, but I believe each province has a Black Hand...? Or was the one in Oblivion a central organization? My belief is that there is one, which administrates the guild on every province. But I can't really say for sure
EDIT: http://www.uesp.net/wiki/Lore:Dark_Brotherhood#Organization you have a lore article on the organization of the Dark Brotherhood
It doesn't actually refer if there are several Black Hands throughout Tamriel. However, if we rise up in ranks in the faction, I doubt that we won't become at least a Finger/Speaker, or even talk with one.