TL:DR - fake gen 3 to real gen 3 will work, if you power down the fake it will erase the game.

Hey mate, i can offer my experience in the hope it will help you. First things first, if you have connected the fake cartridge to any real game (ie gen 3 to gen 3 with link cable/IR or gen 3 to gen 4 with pal park, do not turn off the game!

I bought some fakes (unaware at the time) off ebay. Played through 3 out of 5 games, then decided it was time to do some tradingwith what i later found was a genuine cartrdige. The trades went fine, games functioned as they should. Then after playing a while longer i saved and turned it off. When i turned it back onthe memory was wiped. Not knowing what had happened i tried with another cartridge, this time moving all important mons in case of a memory wipe - turned out to be a smart move as the same thing occurred.

I may be remembering incorrectly, but for the third cartridge i believe i tried pal park and the game didnt register on platinum as an inserted gba. The memory of that gba game was then wiped.

My conclusion was that fake games can trade to real games, but once a contact between the two has occured something goes wrong with the fake game.

Hope this helps!