This is from DigitalOcean’s FAQ
What is your policy on TOR?
You will be responsible for the sub-users that connect to your TOR service. If there is abuse that is a result of your sub-users, we do not have a way to tell the difference, so it will be as if your account was abusive. This will get flagged by our backend and lead to your account being suspended and virtual servers destroyed.
We do not recommend running open services where any user can connect and possibly be abusive, as it will all fall under your account and can lead to service interruptions for you.
We also do not restrict the installation of software, but you are responsible for how it is used and how freely available you make the service.
In short, you can run TOR as they don’t restrict what software you may install on your Droplet, though if an issue arises, you’re 100% responsible.