I believe some people start using DigitalOcean for the first time just because you mentioned it in your Discourse install guide. I think you should also post your affiliate URL for DigitalOcean so you’ll get a referral fee and it would be a sort of contribution to the Discourse.
Or make an agreement with DigitalOcean to pay a referral fee when someone creates account in DigitalOcean and installs Discourse with Docker, for example…
My opinion you should post DigitalOcean referral URL in the installations guides and here.
If they did that people would think that they are recommending DO just for the money. I think the reputation boost is more important at this stage (I could be wrong of course…) while Discourse is still relatively new and unknown.
Digital Ocean only offers credit for referrals, so the only people such a referral program would be useful for are customers of Digital Ocean. If the answer to #1 is CDCK Inc., AFAIK they don’t use Digital Ocean for hosting.