It's what I use and it is perfect emulation and I play pretty much all of the GB and GBC games using my DSi XL the r4 card and the GameYob emulator. Though I would recommend using the GameYob emulator as it works a lot better than Lameboy and it is what seems to be the recommended one over lameboy.

You need a card like the r4 3ds and the lameboy emulator, which is free and you can dowload it from 3ds homebrew app - which is really a ds homebrew app that also works on the 3DS with the flashcart. While you need an extra accessory, you can totally load and play GB and GBC games on the Nintendo DS.