Is it possible to bring back Nagato (Pain) using Edo-Tensei?
My theory:

Sealing 'someone' doesn't mean that they are going to seal the soul of that 'someone'. It is not explicitly mentioned that the Totsuka Sword includes the soul up to the extent like the Shinigami. 

The body can be remained in the "world of drunken dreams" but the soul can be released. Edo-tensei only requires a body of a living person as a vessel, then a deceased person's soul and bound to it. So it is possible that a person struck by the Totsuka Sword can be brought back by Edo-Tensei.

Update: 

As per Kaguya Otsutsuki about Benihisago, It seals the soul as well. Once sucked in, releasing Edo-Tensei won't release the person. Its mentioned here Benihisago.