Hi Paulo!

Unfortunately, the agreement has to be with the operating carrier, codeshares do not apply for ZED fares. If you really want to take advantage of the ZED low fare, and you can get to GRU, you could go JFK-GRU on DL and then GRU-LIS on TAP Portugal, assuming you have some kind of agreement with them. However, TAP does serve quite a few different cities in Brazil with nonstop flights to LIS, I would give that a try. Especially when switching airlines and factoring in taxes, it can save a lot to avoid connections when possible, so any savings you make with the ZED low could be very quickly wiped out when you compare it to a nonstop. Also, I don't know about Brazil-Portugal, but I know that flights between Brazil and the US can be pretty full.

Take care!
-Brian