yes that theory was made befor madara confessed that to obito..
obito doesn't seem to remember anything about his meeting with kisame...becuz it was tobi-madara who met kisame..
Was it ever referenced? At all?
So maybe it just didn't come up. It doesn't make sense to keep Obito in the dark about things involving his body. What if others talk about these things and he feels betrayed? Unnecessary trouble, no?