So we should probably distinguish between a host with puppet master and the rest, or is there better way to resolve "#puppet?". Otherwise we'd mark discovered hosts or hosts not using puppet with warning flag.

I think checking puppet_proxy (sorry, not #puppet?) is the only thing we usually do, e.g. on the host#edit form for whether to show Puppet-related tabs. Host status shouldn't apply to discovered hosts, but I think it's worth distinguishing between a host that should be sending reports and one that shouldn't.