I think saying some resembles whoever their pic base is one thing, but actually referring to them as the person they use for the pic base is another and it's that, the latter that I would take issue with. For instance, in an RP recently I said John Madison looked like Buffy The Vampire slayer, which I think is fine but if I was to refer to him as Sarah Michelle Geller than I would think that would be rather lame and shouldn't be allowed.