The ones by Nyko are officially licensed, so I suppose they're 1 1/2-party, or something.
Memory cards for N64 and PS2 (two systems I own) seem to be practically immune to adverse effects, unless you really screw it up by cracking it open or modifying it. In fact, the memory cards I buy for my PS2 ae practically always third-party, because I'm cheap. Same goes for controllers; Sony hasn't made any wireless ones, so I got them from Pelican (who amke some of the best controllers ever).
And on a related note, I seriously doubt that using third-party hardware voids your warranty. First, there's no evidence that you've used them, so it's not like Nintendo will refuse you service. Unless you're talking about stuff that actually modifies the hardware, it's not aganist the rules.
*cue someone proving me wrong with trivial evidence*