what if the achievements are disabled in the beta build?

I believe the beta application said beta participants would get full access to the complete DLC, including achievements.

I think it kind of makes sense. When it's in beta they have a more focused number of people testing it. This lets them fix the bigger issues before getting swamped with all of the minor bugs that are only going to turn up once the patch is being used by everyone. It just helps to streamline the process a bit.