Perhaps Scully meant that the particular anticoagulant in the creature's saliva is unique to vampire bats, but other animals, such as mosquitoes and leeches, have anticoagulants in their saliva for precisely the same purpose.
Unless the bat nailed to the masked bat harvester's door was preserved through taxidermy it wouldn't remain in such good condition.
Once again, the view through a set of binoculars is represented as a sort of figure 8 shape - that is, two overlapping circles; anyone who has focused a set of binoculars will know that that's not the case.
When Scully speaks with Detective Abbott on the porch, the camera crew can be seen reflected in his sunglasses, clearly positioned behind Scully.