All Dragons in Skyrim will be Jills, just different varieties of them.
Actually, Michael Kirkbride, one of the people who for all intents and purposes shaped the gods of Tamriel into what we know them as today, said that these Dragons are something else. I had assumed, based on what I knew of Jill's functions and what these ones were doing, that they were the same. I'm rearranging my hypotheses with the idea that not everything about Tamriel has already been shown in the last four games.
I've seen the normal Dragons, the frost one, and in the Gamestop trailer one particularly enormous beastie.