Here is how I manage to find hidden player who have their own IFF file (portrait and c-face):
FIRST OF ALL BIG THAX goes to
FlyingFinn for the editor.
Here is how you do it:
1. Open FlyingFinn Editor
2. Open you nba 2k game folder (with all the IFF files)
3. Find the first png001.IFF (the very first png.iff)
4. Now go to the editor again and press twice on any of the players (don't choose a CAP,choose normal nba player)
5. You see the player's ID (Photo,PBP,and ???). Change the player's ID where it says PHOTO to 1 (=png001.iff)
6. Now you press "Browse"

button where you have PHOTO(in the editor) and you'll see a table like this pop up:

7. This mean that the png001.IFF file has no corresponding nba player in the roster file, that means that the player is hidden. In other words
player's IFF is in your folder but he is not present in you roster.
Now if you wnat to see who is there in that png001.iff, you simply change the ID of any player you want to 1 (with FlyingFinn editor), save and launch the game. For example, I take SAMUEL DELAMPERT, open his info and change his ID from 826 to 1. I press OK, then SAVE. Then simply go to tha game load the roster file you have just edited and check, in this case, SAMUEL DELAMPERT. You will see a new player, a hidden one.
NOTE, you check only these IDs, which are in your nba folder.
For example if in step 5 you'll change player's ID to 2 (=png002.iff), you will see that there is no such IFF file in you nba directory, which means, that there won't be a player with a headshape, there could be only his portrait (usually these are legends).
So check only THE IFFs which are in you game folder, that is why you have to keep your game folder opened. Unless you're curious, who are these players without iffs.
I HOPE THIS WILL HELP, and TOGETHER WE CAN MAKE THE LIST OF HIDDEN PLAYERS.