While all RAM is third-party, using the non-Apple selected third-party puts the onus on the owner for potential issues with defective RAM and not on Apple, I still think that saving a few bucks and doing it myself outweighs the risks. Even at that, if the RAM is bad, all you have to do is replace it since, generally speaking, bad RAM isn't going to destroy the rest of the computer.
I have an old C2D 24" iMac that I put my own RAM in, bumping it up to 6GB max, and a 2010 i7 27" iMac that I put my own RAM in, bumping it to its max of 16GB. I also have a 2010 cMBP with my own RAM, 16GB in it too.
All three Mac's have been running just fine over the years and I've never had any RAM-related problems. With that said, the reliability of RAM these day's is quite good and I'd rather use my own, where I can, and save some money over the Apple marked-up RAM.