Yes, that is true, and the impact is visible in some discussions. The paid operators maintain web sites, twitter feeds etc that direct the attention of sympathetic activists (perhaps "fellow travellers"), but a vast majority of them surely are not paid. I doubt that HN has large enough following in Russia or its sphere of influence to attract people that would actually be paid to downvote.

I do agree that it is sometimes frustrating that people downvote without commenting and offering any other views (which, if void of positive contribution, would expose them themselves to downvotes).

HN is exactly the kind of strategic target for these guys. HN is not widely read in Russia, but it's widely read by power users, people who translate and re-print tech news on russian websites, etc. Hell, I'd say that half of decent articles from Habrahabr (one of most influencial russian collective blogs on tech) are translations from HN frontage. So, it's only natural to create a left-leaning, anti-US climate in a website like HN and others.

It's also almost religiously policed by people who don't seem likely to appreciate shills.

Nobody likes shills. That doesn't stop them from being effective.

No, the relentless policing does.