Was the assassin faction in daggerfall the dark brotherhood?
Yup.
Yea this is what i hope aswell. But not only with the Dark BrotherHood and Morag Tong. But then with more such things like. Mage Guild, Necromancy,
The Mages Guild can be the clients of the Dark Brotherhood actually.
The only rivals the Dark Brotherhood could have is a rival assassin guild, like the Morag Tong. But since the DB is already well established in the rest of the provinces, other than Morrowind, they pretty much control the blood money contracts.
And the Law knows well enough to stay clear of them, unless some fanatic guard captain want them down anyways. (Which will result in his eventual death
)
Guilds and nobles alike call on the Dark Brotherhood. They're just business men whose business is assassination. Okay, so they don't care if it's a noble, a child or an old woman, but still.
Business men with an honest trade.
In fact, in Daggerfall, you can be the assassin who will kill renegade mages on behalf of the Mages Guild and even kill Mages Guild members, on behalf again of someone from the Mages Guild.