I know a little bit about how this works, having gone through a lot of drama with Digg myself and having talked to Kevin Rose several times to resolve it. For some time I was also convinced that Digg was saying one thing in public ("Digg is a community-driven site") and another things in private (banning users and entire sites without warning or reason). I've since come to see things a different way, and the truth seems to be somewhere in the middle.
I'm an owner of a site called Blogcritics: this site. We've had a number of articles submitted to Digg. Some by random readers, but many by our own editors. For some time we instituted a program we called "Red Alerts," where articles we thought would be a good match for Digg (and several other sites) would be submitted by an editor and then the URL listed on the article page so that registered Digg users could more easily vote for the article.
We also sent out emails to our writers via a group we use for site-related communication, inviting them to read the article and vote for it if they found it worthy. I personally voted for many, but not all, of the articles "red alerted" in this way. I'm not entirely sure how many votes it takes to reach Digg's front page, but I'm quite certain we never bullied our way on to it.
At most I believe we had around a dozen people I recognized as site members voting for articles, and it takes at least three times that to make it on to Digg's front page. What those votes from multiple people did do, however, was raise the profile of the submission in Digg Spy, which is where a lot of people look to try to filter through the tons of submissions. Every time someone votes for an article, it pops up in Digg Spy, and people scanning the list get another chance to click and check it out for themselves. Most of the articles we submitted never made it to the front page, but some did.