Gideon is not a vampire.
When Gideon is animated, there are two competing continuous effects trying to modify its type and or subtypes, so two effects that apply in layer 4.
If several effects apply in the same layer, you apply them in timestamp order, unless there is a dependency, in which case you apply the independent effect first.
The whole question is then to know if there is dependency between “becoming a creature” and “becoming a vampire.” Even though the result of “becoming a vampire” is different whether you apply the “become a creature” effect or not, what matters in order to have dependency is if what the effect _attempts to do_ is different. Here, what the effect attempts to do is setting the object's subtype to vampire, and this doesn't depend on whether the object is a creature or not.
The two effects are therefore applied in timestamp order. First Gideon becomes a vampire (which has no effect since it's not a creature nor a tribal at this moment), then it becomes a creature. In the end, it's not a vampire.
Daniel Kitachewsky
L3, Paris, France
MTGRules-L Netrep