Why assume they would sweat blood? We don't. Nor do we sweat hamburgers, french fries and pizza (or whatever else we've been eating). Sweating blood makes very little metabolic sense -- there is too much in blood that is too valuable to lose that way.

I was thinking temperature control -- we sweat to try and maintain a temperature. Do vampires need to maintain a temperature? If so, what temperature? Is the range wider or narrower than for humans?