That question is 2 years old, and refers to an "unlimited bandwidth" fair-use policy. DO does not have unmetered bandwidth, so is it still relevant?
Their current policy FAQ says they do not even explicitly forbid Tor exit nodes, although there is a stern warning, so why would they disallow a proxy configuration dedicated solely to your site?
I'm assuming that's a paid CDN with clients like CloudFlare or Akamai, not you distributing your website to multiple datacenters in order to serve more clients faster. If you happen to use CDN like DNS features to route the client to the closest Digital Ocean datacenter, you're probably in the clear.
