As far as I know, it still hasn't been proven that there is a homozygous spider or pin (i.e. one that produced a large number of only the mutation bred to normals). Maybe the homozygous just hasn't been produced yet or hasn't been grown up and breed yet or it just hasn’t been shared publicly but it's also possible either or both mutation might be homozygous lethal and a homozygous animal will never hatch or might hatch but would never grow up and breed.
Until we have a homozygous animal we can't know what it looks like to really say for sure that either of these mutations are completely dominant.
If both parents are spider or both pin I suppose you could call the mutant babies 33% chance homozygous but even that might be questionable without the proven possibility of a viable homozygous animal. If only one parent was spider or pin then there would be no chance the spider or pin was homozygous.