Yeah, good point. Any lenient DM would probably allow it.
But by RAW it is dubious, there is no "vulnerable to sunlight" clause in vampires, (and neither do wraiths), so it isn't a rule term, but a normal English one. So then it's left up to the reader with vulnerable means, but again I agare with you. Also Sunlight does not cause penalties so that sentence shouldn't do anything, but that's nitty gritty word lawyering. But it proves the idea is there, the words just fail to make a clear distinguishing between the lesser sunlight penalties (Light Sensitive and Light Blindness) vs the greater sunlight penalties (Sunlight Powerlessness and whatever Vampires do).
But I am way too offquestion, so I keep quiet now, if you want to debate further start a topic or PM me to start a topic. I see a really silly argument that leads to Cloak of Shade protecting vampires, but I don't really want to go there because it's a silly argument to defend.