Board Thread:Lore Discussion/@comment-25343239-20150128215539/@comment-24755309-20150129003215

that is much better. Anyhow, Nocturnal is able to use the gate thanks to the skeleton key. If the gate is not open, then she cannot go to Nirn. The thing about the Dragonfires is that they seal the barrier between Oblivion and Nirn. This means that Oblivion Gates cannot open while they are active, but the ebonmere is an exception, being held open by the skeleton key, thus not affected by the dragonfires all that much. OR, since she never appears again and the ebonmere is merely to allow thieves good luck, Daedric Princes are able to appear, but only through the use of a gate and only for a few moments.

Sanguine did use a gate. The portal to the Misty Grove.