I hadn't thought about this before, but I think you are on to something David. Given then lack of a sort of cultural-awareness of animal welfare, I do think Tezuka's works are forward looking.
He definitely comes from the Buddhist perspective that all life is life, no matter how small or large.
Honestly I think Plague Dogs could have a good theatrical running in Japan (despite its age). It is still beautifully animated (this would be more appreciated by the Japanese than Americans), and I think people would appreciate the message of animal suffering more there than in the US (the relation to Pom Poko is very real). I also still think of the response to the showing of Gojira back in the 50's, when people left the theatre in tears for the sake of the monster.
It is surprising to me that Japan doesn't have any sort of institutionalized animal welfare program, especially given how sensitive their media is to the suffering of all the small things.
Edit: BTW, I think you should consider Jungle Emperor Leo. I appreciate how Tezuka considers this possibility of animals taking human consciousness (perhaps this is sci fi?), and while he suggests some ideas being adopted, other ideas cannot. This is where I think Leo having birth and death is important, animals still remain animals. They have a little time to be, a little time to struggle (for what is right, in the case of Leo), but lifetime comes in decades, ideals must be reached across generations. Humans can see three (or more) generations of these lions, and their suffering and struggles are no less than ours.