Yes. The difference in terms just highlights a difference in emphasis. All zen teachings basically point to the same thing. The difference is dependent on what obstacle the teacher is pointing too. For someone who is always striving, a teacher might call it original mind to emphasize that he is already in possession of what he's striving for. For ...
You can answer "yes" based on the following reasoning:
Essence of Mind is grounded in Dharmakāya
Dharmakāya is the unmanifested, "inconceivable" aspect out of which Buddhas arise
therefore, Buddha Nature arises from Dharmakāya
therefore, Essence of Mind = Buddha Nature
However, you can also answer "no" based on the equally ...