So far no one has come forward publicly with a proven homozygous spider. It could just be that not enough spider X spider breedings have been done yet to produce enough homozygous spiders for one to be bred enough to prove. Or it could be that spider is a homozygous lethal mutation and each egg from a spider X spider breeding has a 25% chance of being a non viable homozygous spider.
I've not heard of homozygous spiders being deformed but since we don't have an example of one we really don't know what they are/would be like.
For now it's a fairly safe bet to assume that any spider you have is only heterozygous for the spider mutation. As with any het X het breeding the odds for each egg are 25% normal, 50% het, 25% homozygous. So spider X spider can not be expected to always produce 100% spiders because of the 25% normal odds. The big question from above is what happens to the 25% homozygous odds.
Personally my choice is between breeding spider X spider and pastel X spider. On the one hand I would like to produce a spider X spider clutch to see first hand any evidence regarding the long running homozygous spider question. But on the other hand I know that spider X pastel makes an awesome combo so that pairing is much more attractive to me. If spider is a homozygous lethal gene it will be almost impossible to prove. With woma we can reasonably assume that the non viable but very different looking pearls are homozygous woma. But if homozygous spiders die before hatching then you would never know if those where just bad eggs. And if spider is actually dominant like pinstripe then you would have to keep back all the spider babies for years to breed in hopes of proving one and if none of them did prove homozygous you might just have missed in the original spider X spider clutch.