the bolt pattern is the same, so why not?
they say that they are gt specific because they will fit on the gt's stock 15s. that means that they will also fit onto the gts's stock 16s. if they have rotors that are gts specific, that probably means that they wont fit onto the stock gt 15s, because they are too big.
in other words, you can probably use gt rotors on a gts, but not gts rotors on a gt.
the keyword there was probably. i am not completely sure if it will work.