It amazes me that there are 5 pages of people who have never posted anything on the forums.
I imagine quite a few people register solely to receive chapter updates by e-mail, without having any interest in posting at the forums. Plus, all forums get people registering without posting. You'd be surprised how many people make accounts at places and never do anything with them.
Is it fathomable in Ouen for humans to (rarely) marry Pokémon? (particularly humanoid ones like Machoke.)
No. There's still a massive taboo against intimate human/nonhuman relations of any kind, though with developments like Fury the Hitmonchan that might potentially change in the future.
Are Pokémon used commercially (in technology, electricity production, to purify plumbing, etc.) in Ouenn, or are they mostly treated as intelligent animals in the scheme of the economy?
Pokémon trained by human employees are used commercially for various tasks. Commercial computer systems have their own Porygon, Water Pokémon are employed by the fire department, etc. Electricity production in particular is not practical, however, as Pokémon can't produce a constant flow of electricity for very long without becoming exhausted; you'd either need completely unmanageable numbers of Pokémon or to overwork them far beyond the point of abuse.