How do you think Team Aqua/Team Magma, as environmentalists/ecoterrorists, would react to Oreburgh City and its reliance on coal?

Well, are they environmentalists, though?  Team Magma in Omega Ruby seem very much not to be; Maxie is a proponent of human progress at all costs.  I don’t think he would be bothered by it in the slightest, and might even own shares in the bloody coal plant.  Team Aqua is a different story, because they do have a kind of cultish devotion to the primordial purity of nature, but they also have a rather obsessive focus on the ocean, not the land or atmosphere, so while I suspect they’d be bothered by coal plants, it might not be high on their list of priorities.