We were planning on it. But being my car had only 2000 miles on it they were in great shape. But with some milage on them it's best to go ahead and replace along with the seals. I'd also look into the Nismo differential cover with the cooling fins. I should of picked one up before I had this installed.
Here's a link for the part number. Which can be had at any dealer. Just confirm with Nissan this is the right part though.
BEARING-DIFFERENTIAL SIDE - 370Z (Z34) 2009+ :: Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com