Well, while it often doesn't seem like it, I am not a real adherent to the "Moe is and was behind everything" theory. But I also don't buy that the Kyudea conversation and events were Kellhus in control and Moe simply being out-witted in a sense and overmatched. I feel like Moe had conditioned Kyudea and was ready and that events never were completely beyond what he had figured, even if they possibly didn't turn out exactly as he wanted.
That being said, Meppa's lack of memory is, in my mind, one of two things really, either a total red-herring or deeply meaningful. I don't see why that red-herring would even need to be there though, Bakker doesn't seem like the kind of author just to put things in there to just fuck with us. Therefor, I feel like Meppa's origin is important. The other most important Cishaurim that we know of was Moe. Therefor, a Moe-Meppa connection seems plausible to me, even if it raises some odd questions about the Psukhe, soul transfers, and Cnaiur.
I just can't believe that Meppa stumbles out of the desert a very powerful Cishaurim with no past memory and that isn't something very important. Even if Meppa isn't Moe, I still think something was up with connection between the two, somehow. There is the possibility that the rest of the Cishaurim, realizing that Shimeh was lost and the rest of them doomed, hid Meppa, but that doesn't really fit with their MO, in my mind. I could see Moe doing such a thing though.
Then again, we could just be off and Meppa really is sent by the Solitary God and his vast supply of Water true divine dispensation. Why lose his memory then? Well, so that he'd be singular in his purpose of representing the Solitary God.