GameShark and action replay are the exact same thing, it's just the name that change between countries...
Codes should work, but don't forget that action replay codes are usually for european systems with european games and gameshark for US/Canadian systems/games, rom data adresses change between US and euro roms (mostly because of translation/bugfixes) and so code don't work out of the box...
But it's rather easy to find the euro or US equivalent of a code, just find online a cheat for both US/EUR version of the game and seek for the differences like if the US code is XXXXXX80 (XXXXXX are hex data of the code) and the euro code is XXXXXX70 then you only have to add/sub 10 (in hexadecimal) to any code to translate them from US to EUR EUR to US.
This method worked for pokemon gb games for me, I can use any US code on euro games.
EDIT: beaten by alphamule .