You can play as a deathclaw in the entire Deathclaw Desert series made by Max-Violence. Otherwise in the regular campaign, you can have some deathclaws join your squad later in the game after mission 7. No MP to SP characters, its a different format.
There's a campaign editor FAQ at Duck and Cover that tells you how to insert self-created characters (beside your main character) into the single player game. I don't have the link, but it shouldn't be too difficult to find.
