The DM Client will very likely not ship with the game. There just isn't enough time to finish, test, and polish it before launch and we don't want to ship something that sucks.

We do have plans to release one, but I don't know when it will be available.

Update: Further comments from Feargus himself:

On the subject of the DM client I did want to say a couple of things: 1) We at Obsidian know the importance of the DM client as it relates to the running of PWs. We want PWs to exist for NWN2, so we need to support the DM client. 2) We are going to be talking over the next couple of weeks to see what we will have at launch and when we will have a more final roadmap when it comes to the complete DM Client. I do apologize for this being the way the information got to all of you about the DM Client, it's not what we intended. I was planning to have us make an announcement in the next few weeks about it, after we had gotten some more of our planning done.