Yes striker is the same as star but nickel is more of a cover CB.Isn't the nickel traditionally more a pass defender while the striker/star needs to be a little bigger for greater run support and bigger bodies?
On run downs it is Striker or Star (Gil) but on passing downs its more Nickel (probably Couch). Unless ur UGA and u got a huge stud like Stevenson that never really needs to come off the field.