i have a predisposition to never want any spiders or morphs

[Seven-Thirty]

This is not entirely correct. First complete dominant is to incomplete dominant as poisonous is to venomous.

Dominance is not only that the heterozygous from looks just like a homozygous form, but more importantly you will have a homozygous which is phenotypicaly identical to a heterozygous that will produce 100 percent heterozygous animals when bred to an animal not carrying that gene. In this case if spider is a dominant morph you should be able to produce an animal that appears to be a spider but will produce no non spider offspring. Following if the homozygous is in fact lethal there is no way to prove Dominance short of finding and preforming genetic testing on a dead homozygous embryo.

I know the terminology of co-dominance and incomplete dominance is wrong but the way it is used in the reptile hobby they are used interchangeably. You also basically reiterated what I just said with different terminology. i.e. super spider that looks the same as a normal spider aka same phenotypes. I was just assuming that people asking the question about super spiders know what super means so I didn't bother explaining it. My bad. XD

If the homozygous is lethal it is automatically not a dominant trait. Every homozygous lethal is technically a co-dominant/incomplete dominant due to the different phenotype. i.e. death. For example, munchkin cats have a homozygous lethal. Homozygous munchkin cats fail to even gestate so performing genetic testing on that is out of the question but it is known that it is a homozygous lethal.

So if you produce a 'super spider' will that result in a slug, an infertile egg that looks good, or does it develop into a white snake and just perish before it hatches?

In theory yes. Any of those outcomes would happen to be the case except the infertile egg part. What seems to usually happen is that the egg will be good but will die before hitting even the embryo stage. It's rare to get the white snake in general in that pairing.