They are not the same:
x = [2, 3, 2, 3]
unique(x) # [2, 3]
unique(Ref(x))[1] # [2, 3, 2, 3]
unique(Ref(x))[1] === x # true
Note that unique(Ref(x))[1] just returns x, since Ref(x) is equivalent here to a vector with a single element x.