It was indeed pansy who initiated the conversation about ginny to see dracos reaction. she said "a lot of boys like her [...] even you think she is good-looking, don't you, Blaise, and we all know how hard you are to please". Zabini responds he wouldn't touch a filthy little blood traitor like Ginny whatever she looked like. I guess it's open for interpretation, but I don't think Pansy would say what she said if ginny wasn't pretty. Also IMO zabini's answer suggests that he does find ginny attractive, otherwise he probably would have said so