yes and no
Rip them down the length first.
Be cautious with a warped board on the table saw so that it won't twist during your cut, it may kickback. You must have the straightest edge against the fence. Tape a block to a corner if necessary or if the warp is severe use a circular saw or handsaw or bandsaw.
Place them side by side and see how the mate up in the center.
There should be no gaps or angles when mated properly.
Take another very light cut along the edge using a sharp blade and pushing slowly forward so as not to force the blade to one side IF they do not mate up cleanly. It's like "jointing" them only on the table saw....which must be dead on accurate and a fence that is secure.
If that's not possible your remaining choice is a hand plane and you can mess them up in a hurry if you are not proficient with one.
The planer sled is for jointing/flatting the top and bottom surfaces, not the edges. So, no you won't need one for this project. However if the cup is severe you may want to plane one side of each board before mating them up ... hard to tell over the web just what you are up against.....
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 12-23-2013 at 12:21 PM.
Reason: added caution