I'm a little confused at something - I know that Google wants all pages of a website to have been linked from at least somewhere else within the site...but what do you do if you're setting up several dozen landing pages for an Adwords campaign? Is it safe to leave them as "hidden" from the rest of the site?
I setup my landing pages so that they are not linked to by any other page on my site--effectively "hiding" them from the rest of the site. I do make sure that the links on the landing pages lead to other parts of my site. Leaving the landing pages "hidden" is very typical behavior and should cause you no distress. Good Luck.