Unlock Busta Rhymes:
Just create a player with the last name FLIPMODE. Then just go to the free agent pool for Busta Rhymes.

Unlock DJ Clue:
Just create a player with the last name MIXTAPES. Then just go to the free agent pool for DJ Clue.

Unlock Ghetto Fabulous:
Just create a player with the last name GHETTOFAB. Then just go to the free agent pool for Ghetto Fabulous.

Unlock Hot Karl:
Just create a character with the last name CALIFORNIA. Then, check the free agent list to discover Hot Karl.

Unlock Just Blaze:
Just create a player with the last name GOODBEATS and then check the free agent list to find Just Blaze.