Neither the Ninja nor the Warlock are Open Game Content, but the two abilities that you mentioned, Sneak Attack and Uncanny Dodge, are definitely Open Game Content (because they're part of the core Rogue class for D&D), so I will elaborate on them.
The rogue's Sneak Attack ability is the ability to inflict extra damage on an opponent if you can catch him flatfooted or in some other situation where he's denied his Dexterity bonus to AC, such as when you're flanking him, successful on a feint for your previous action, or if he's hung up grappling someone or trying to climb something. There may be other situations where you can gain this bonus, but these are the ones that jump to my mind.
The Uncanny Dodge ability, which the rogue gets at mid-level, allows you to keep your Dexterity bonus to AC when you're flatfooted or otherwise not immobilized in some way, protecting you from most situations where you are in danger of being sneak-attacked by another rogue. You can still be flanked (and thus sneak-attacked) unless you have Improved Uncanny Dodge (which you get later on), and even with that feature, you can still get flanked if your opponent has at least four more levels in rogue than you do.
