I saw this, but I have Palit 2600pro(with ddr3 memory) card and in GPU-Z i have also unknown subvendor.I hope that new GPU-Z will recognize it.I don't know is sapphire have subvendor(but I'm sure that have), because I could change it for sapphire card because fan on the palit is became annoying.
Also as I know 2600xt have higher clock then 2600pro with ddr3 memory(600(palit) or 700(sapphire) ->800 MHz for gpu and 1400(700)->1600MHz(800) for memory), and if you see much greater clock thean default you can be suspicious, but as I know volmod on palit and sapphire could be done by pencil and higher clock could be easily achieved, and this method is not precise.
And, yes putting 2600pro bios on 2600xt card and publish that score as score of 2600pro is cheating.