The show seems like it's going to have many cases of this. Vance from the original NCIS was in the first episode. Makes sense when you consider he's the director. He's already been confirmed as a recurring character as a result. Pauley Perrette has also made appearances as our favorite Perky Goth.
The Pete Best / The Other Marty: Louise Lombard played Lara Macy in the NCIS backdoor; when the series went into production, Macy was dropped and Linda Hunt's Hetty was added.
Real-Life Relative: The main ship of Deeks and Kensi, becomes quite hilarious when you find out that Daniela Ruah is married to Eric Christian Olsen's stunt double. His stunt double? His brother David Paul Olsen. Not only are they brother and sister-in-law, but her husband is also on set to watch their shipping.