Looking at what reddit does, I seriously doubt this. They're not a "publication". They don't have to pay writers/journalists to create content, the content comes free. There are many ad-based sites that don't have that luxury. Event moderators come from the community, they're only significant costs is infrastructure and payroll. I use to work for a company that has a fraction of the uniques reddit gets (still in the millions a month though) and that 1) does a lot more then reddit as a product and 2) has significant other costs outside of salary and infrastructure and was still not in the red. Also, this wasn't shitty advertising, the ads were well monitored and we broke ties with networks/advertisers that we found continuously had crappy ads.
There's also no control over the content. As an advertiser, I would be worried with where my ads may end up. With a traditional publication, I generally know the type of content that will come out and their policies.
For your publication, the writers will keep writing as their job, but if you upset the content generators at reddit, you'll lose your content source.
In general, monetization of a publication is a more proven model than monetization of user generated content.