Is Rashi on the Rif the same as the one in the Gemara?
If it is, why is it put there?
If its not, then why did Rashi write a different pirush on the Rif, and does it have a different Derech then Rashi on the Gemara?
The Rif has written his Halochos from Yerushalmi as well as Bavli and there is a Rashi commentary on that (in the Rif) e.g. see Berachos 8b (Rif pages) on the last of the narrow lines where he quotes the Yerushalmi and Rashi has a commentary on it - so for sure it's not exactly copied-and-pasted from the Gemara, in fact there are times that the Poskim quote the Rashi on the Rif because it's not in the Gemara.
As far as style it is the same.