Actually the two parasites the OP has highlighted are created simply by signing up on those websites and taking advantage of the options they give to logged in users. No hacking involved.
For Gitlab sites, you just need to find installations that are open enough to let you post a project, and then you can create parasites via a number of ways - I prefer the wiki route, but the movies guys seem to prefer the issue trackers. For the viki.com domain you just need to sign up and post a 'collection', putting your parasite content as the description (though it doesn't actually give you a link so the end user has to copy and paste from that - useless).
As for ranking, check their backlinks. The Gitlab site uses links from a number of movie PBN/news type sites (check the source, they're linking out to a load more parasites), while the viki.com parasite uses plain olde spam, guestbooks and the like.
