Very interesting read and sounds very plausible. However, knowing that the anime is based upon the original video games, the theory here does loose merit. For example, there are other kids similar to Ash in other games with the same dreams but with no rat to accompany them (at least I think so, I gave up after red/blue/yellow).
However, this theory could also easily apply to the kids in those games too. I'm only basing this over little experience playing the later Nintendo DS incarnations and GBA ones, but the protagonists are always some new kid moving to a new area, or reaching some form of maturity at the start of the game, and then adventures in a very PG world where everyone does rely a lot on pokemon, like Ash does in the dream-theory.
Interesting food for thought, and surprisingly, it makes the series (game and anime) a lot more easier to understand for me.
