The only thing that he wears that can affect you are (except auras ofc) magic find and gold find.
The GF is always applied, both to your kills and the mercs kills. It also works both ways.
The mercs MF however, only works if he gets the kill.
Archone normally I agree with you, but maybe I misread your post. Did they change GF? I thought GF worked exactly like MF when it came to having your mercenary equip items that add to this. In other words when you make the killing blow or open a chest only your MF/GF is used. When the mercenary gets the killing blow their MF/GF is added to yours.
Edit: I ask because according to the wiki:
Originally Posted by http://diablo2.diablowiki.net/Gold_Find#Gold_Find_Strategy
Merc kills add their GF to the player's, but it's not generally worth it to wait for them for the small increased %, you could simply kill more monsters in that time, which would yield more total gold
Edit#2: @jatna the wiki is a good source for info on these types of topics. Here is a link to the Mercenary Guide. Good luck with your characters.