However, he is only available in Serious Sam HD: The Second Encounter if the player has bought the Serious Eight DLC. Otherwise, it is impossible to use him. Since it is not possible to get the Serious Eight DLC, those who don't already have it won't be able to use him at all.
White Whytee's model can be found in the Serious Sam HD: The Second Encounter game files even without the Serious Eight DLC. This suggests that he was supposed to be in the game from the very beginning, but was cut for an unknown reason.
This model is obtainable if you buy the retail version of the game.