Spiders are heterozygous, but they are a co-dominate gene. If the gene is present, then it will be apparent.
It is impossible to have a het. Spider, because when a morph is referred to as a het., it usually is referring to the animal being recessive heterozygous, which contains the gene for the morph, but it does not show because it needs to be recessive homozygous to be apparent.
Plus, if there is no proven homozygous super form, that means that it is more likely that it is a dominate gene. :]