On https://www.cloudflare.com/abuse/, how about stating Cloudflare's policy for investigating spam-vertised Web sites that are proxied through CF? The page mentions malware and copyright, but not spamvertising.
The "general" category would be the correct place to report that. We'll review the report. If we can verify allegations we'll take appropriate steps, but at the very least even if we can't necessarily verify the allegations we'll notify the host of the website.
I'm Justin -- Cloudflare's Director of Trust & Safety.
Happy to review/answer questions.