I don't think that specifically Rasputin appointed Exos as Seraph agents. The 1st generation of Neomunian humans were raised by Exos on the ECHO-1 ship. You bring up a really nice speculation, but I think almost all evidence points to Rasputin not being tied to actual creation of Neomuna but rather Soteria is the one. The only reason Rasputin has knowledge of Neomuna is his ties with Soteria (they communicated at different points). I can definitely see how you made the connection though. Even with all his subminds tied to different planets of our Solar system there is still only one Rasputin. I think Bungie made that retcon and point clear that's how they want it to be. Still will be interesting to see.