The Entity is part of the story arc for the Sith Warrior on Corellia. The Jedi Entity is the Jedi Knight formerly known as Jedi Exile or if you prefer, Meetra Surik; They're not the same character.
Also, the Exile is seen and / or heard during the Taral V and Maelstrom Prison flashpoints, as well as during a conversation with Jedi Master Oteg, which is a part of the mini-arc storyline, surrounding Revan's rescue.
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Either way, pretty sure I've seen an interview where Karpyshyn acknowledges that the Entity is indeed Kreia herself, even though he also says that the storyline or that particular bit wasn't written by him.
Yeah, I know who the Exile is, as I said... I forgot about the Entity though... Hmm... I don't recall that part with my Sith juggernaut (he was light) but I'm now doing a sith marauder so I'll see it again soon, she's on Quesh right now.