Indeed. The Giant even acknowledged the possibility of A Good vampire in Stickworld, but didn't really care because that's not going to be in the story.
As for liches, it's surely possible, but given that the act of becoming a lich is unspeakably evil and is willingly undertaken, all creatures who become liches are almost certainly evil at that time. While they may become better after time, Xykon certainly wasn't, and the Sapphire Guard had Roy to attest to that as well as their own scrying. They had every twin to believe that Xykon was coming to destroy them and zero reason to believe he wanted to negotiate (and even if he did, they had zero concessions to make to him).