I would say it's better to be aware and ready than to assume they aren't, although I'm sure statistically some are less bloodthirsty than others.
[Of course that would include those like himself seeing as humans don't see any difference at all between Fallen and Sangarde.]
If they are indeed "good" vampires, the question would stand as to why they've been imprisoned here. Being a vampire doesn't make you a criminal, after all.