Guild Wars: Skills and Campaigns?

I recently bought the Trilogy pack and began playing and have not yet purchased EoTN. Given if I purchased EoTN, would I be able to unlock EoTN's skills if I used skill merchants in other campaigns(like Nightfall, since I started as a Dervish)? Or must I enter(and purchase) EoTN with my dervish and buy skills from those merchants in order to receive EoTN skills?