Why not? PoW challenge doesn't whitelist botnets. If the dumb scraper makes only get requests and doesn't solve the challenge, it doesn't matter how it connects, even if it's a perfectly hidden tor exit node.
Because the work would be done by the compromised residential device. No bothnet owner is going to care if their 100,000 rooted routers have to do a little more work. It’s still “free” from their perspective.