YAY! My account has been frozen since January, but I clicked the link anyway (despite "(...) to active accounts" part), and was shown a battle.net page with "try
Mists of Pandaria for 7 days" promotion. Which is interesting, because I already had both added MoP to my account when it was not included in the Vanilla package (in January, when it was on sale), and used the MoP 10-day trial (right before that purchase). Anyway, the link worked, and I now have 7 days of active account. Which is kind of unfortunate, because I can't play next week and was going to set up my WoD subscription a bit later on.
So, you might want to clarify that "to active accounts" applies to frozen accounts as well.
EDIT: I am
EU and clicked the link on the front page of MMO-C. Worked for me.