After a few seconds of searching the web, I have determined the following: to sign up for Wildstar raid testing you need two things.
1) You need an active gaming community with at least 40 members.
2) The above mentioned community must have a website containing information about raid times, member contact support, etc.
On the Wildstar Online beta sign-up page you need to paste the link into the entry box in order to indicate the guild/community to which you belong.
That’s it for now. Beta-3 begins in December 2013; good luck!