Like all social media / user generated platforms, paid promotion is constantly being passed as legitimate content in some shape or form - but there's not really any reason to believe that reddit capitalizes on that themselves.

To look at how reddit is monetizing their platform, it seems straight forward to look at their advertiser page, and see how they try to pitch their ad platform. Paid promotions - which have become somewhat of a first party feature on Youtube for example -aren't discussed.