DO absolutely allows (and encourages) resellers and SaaS platforms on their service. My day job is with DO and Dply was built as a side project to meet some needs I have heard from developers, students, and open source projects.

Dply operates with DO's blessing but is otherwise unrelated in any official sense. We launched under a credit like those offered in the Hatch program for startups: https://www.digitalocean.com/hatch/