It's amazing how that picture of a fossa so well shows incredible similarities... the legs are quite remarkable. I'm not sure about the ears, and it's awful hard to tell with the lighting but there may be a subtle difference in color. These sort of changes MAY indicate some speciation, but hardly justify the sort of headlines this generated, which made it seem like the discovery of the Platypus, or the Echidna, or something like that.
"New Carnivore Discovered" sure is a lot flashier than "Obscure animal seen wiih unusual colorations that might suggest speciation."
I don't think the WWF faked this, I think they simply did an amazing job of spinning a none-too-remarkable sighting.