No, Ceridwen's sphere is dimensional magic. Oghma's sphere is metamagic/knowledge. Ceridwen was responsible for binding the worlds together (and, later, also riping them apart). This ability also probably also allows her channel the magic from the all planes of all the different spheres for sorcerers to use, while most gods can only channel power from the planes of their own element. On the other hand, Kael has stated that mortals can only channel mana from their own plane, so that might not be right.
I personally like to think that she doesn't really have a vault of her own, but instead control all the space linking all other universes (the Nexus, maybe?)
While gods have an extremely strong connection to their spheres (and themselves act as portal though which the power of their sphere can be channeled, with or without their consent), I'm not sure if their power is really exclusive. The divine spark from Nemed, the original god of life, if what lets humans channel every sphere. Also, Auric Ulvin, the reincarnated God of Winter, channeled Sun magic to escape from the Shadowed Vale.