You should be able to use any DNS services you like for this, including what is offered via Oracle Networking. You can check out this walkthru on getting started with email delivery via Oracle - https://docs.cloud.oracle.com/en-us/iaas/Content/Email/Concepts/troubleshooting.htm?Highlight=email%20server
Oracle + Dyn
Are you sure that I could use any DNS service for this? Because usually the PTR record works only if it's set on the DNS server that is authoritative for the IP you're using, and in this case those are oracle's nameservers. Do you think that if I use my own DNS server it will work? Because I tried and it didn't, but since I'm new to DNS management I could have done a config mistake.
EDIT: I gave a quick look at the docs you linked, but I'm not using Oracle's Mail Delivery service: I'm using a Mailu docker container running on a vps.
I tried setting the PTR record inside Oracle's DNS service and I can confirm that doesn't work. Out of frustration I created a free mail account for my project and gave up, for now, the idea to have a personal mail server. If I'll try again in the future, I'll use Google Cloud or Digitalocean, I saw that both have documentation that explains how to set up a PTR record to their IPs.