I managed to find that the checksum used for the NHL2K11 save game is a standard CRC-32 checksum. The checksum is positioned in the first four bytes of the file and is calculated from the content of the rest of the file, excluding these 4 bytes.
So what does this mean?
This means that we can have a roster editor for NHL2K11!
This is the first edit done to a NHL2K11 save game outside of the actual game with a custom calculated checksum that the game accepted. Say hello to William Nylleter: