So far, it appears that Hypo A and Sunkissed are cumulative, as well as Sunkissed with Ultra. I suspect that Hypo A and Ultra will not be cumulative, but don't have any hard evidence on this. Just flimsy evidence based on breedings I did in the past with the original Ultras I had. From the results I got, my suspicion is that at least one of the group was homozygous for BOTH Ultra and Hypo A simply because of the, then, curve ball results I got. For the longest time I thought Ultra was simply Hypo A, because I KNOW I bred one of the Ultras initially to an Amber and got all regular Hypos. Then in later breedings combining Ultra with Hypo A, I got Hypos as well as lighter colored variants, which threw me for a loop for a while. Now I suspect that those Hypo parents were simply het for Amelanism, and those lighter specimen offspring are Ultramels. Some of those should breed this year, so they would be Ultramels het Hypo A. Perhaps even homozygous Hypo A, but that is only a possibility and NOT a probability at this point.
However in other breeding trials, I have bred a few Ultras to Ambers and gotten all normals. Yeah, this is part of the reason I was scratching my head wondering what in the world is going on. The problem is that as best I could tell, there was no distinctive visual difference between those Ultras and the Ultras homozygous for Hypo A. Now, this has not resolved ALL the confusion with Hypos around here, but I think this is the answer to at least part of it.