That's not quite right. That isn't how most people cure their rock. To answer your question is no, you don't need a skimmer right away. Actually, you don't need a skimmer at all but I would highly recommend 1. If you could see what my skimmer pulls out, you wouldn't want that in your tank either.Nope you don't need a skimmer.
I think most people just put the rock in a bucket with a strong powerhead and do water changes everyday.