I cannot imagine that there are very many people, more than two or three, that would spend money and time on multiple accounts for the purpose of being able to place more down votes on things. That just doesn't pass the smell test.
The first thing that comes to mind when I think about accounts with supporter status that don't participate is that they are people that want to avoid ads, or to support the site that they visit. In some cases it's probably a combination of those things.
Anecdotally, I lurked here for a couple of years before I created an account. During that time, I sometimes felt a bit guilty that I was coming here for news and entertainment and giving nothing back to the site. So, I created an account and started participating. That made me feel like I was not just taking. Later on, my desire to further support the people that do the real work for the site, combined with my desire to not be bombarded with annoying ads, caused me to subscribe as a supporter. I can imagine many scenarios where I could have just skipped straight to supporter, rather than participant. In fact, there are lots of people that don't like to get involved in discussions online because they often turn into train wrecks. But, that doesn't mean those people don't want to show some support.
Anyway, I'm not going to say that nobody is doing this secondary supporter account thing. I just can't imagine that it's a widespread issue.
Even if it's one person doing it between two accounts, that's x8 voting power (if they have gold) which is pretty significant given the size of VGChartz currently.
Not Supporter related specifically but we've had users in the past who have created multiple alts to upvote/downvote things To clarify, this is something we knew what was happening for sure, we dealt with it, we confirmed it with Trucks (or Talon, I can't remember).
It wouldn't surprise me if there's a few more, I have my suspicions on two, I have to do a little more digging if I can be bothered, don't really care if the alt isn't being used but upvoting/downvoting abuse is using it.