It's been noted in other topics (cba to find links) that yes, it does indeed work, also with flash cards that did not EVER have any 3DS support (R4 Revolution for DS, for example, all the old crap).
But then you have the cart sticking way out like a PassMe. No bueno.
Edit - you'd be better suited spending your money, however, on something that DOES natively work on the 3DS, like the R4i Gold from r4ids.cn or the Supercard DSTWO.
http://www.walmart.com/ip/Nintendo-3DS-Action-Replay-3DS-DSi-DS-Lite-DS-Nintendo-3DS/22254553@Sicklyboy Yeah to buy an AR solely for this its kinda pointless but if you already have one sitting around then it can hold you over until you manage to get the money for a new r4. The AR is kinda bulky but that's not all it feels like it will snap from nearly anything I don't suggest you buy one unless you plan to use it to backup game saves via sd card. @Rydian what kind of r4's are you talking about most of the r4's i see are 12-13 dollars for a single unit and a AR is about 15-20 bucks.