Yes, the DLC characters should be banned from tournament play for at least a month.
However, my only concern is what if a month after their initial release, they're either still broken or they were patched, but something else arose from that which caused them to still have something stupid. Do you just say, well, the month ban is over so let him/her rock as is and hopefully everyone knows what they're up against? Or should other measures be taken at that point? Perhaps then having that character pushed to a two month ban to ensure that they get fixed or understood correctly?
I do like the idea of banning them from tournament play as I feel like it would force NRS to do a better job of releasing new characters and would make sure that they patch/hotfix issues at a more frequent pace if they want these new characters to be showcased/hyped up.
Also, for those saying, "No, I want to see them in tournament play asap, for hype"; Is a 1 month ban really that bad? I mean, after the initial month of DLC release, you'd be seeing a new character(s) in play every month after that and be more hyped to see what everyone has cooked up with said character(s).