Yes, you're supported
However, apex 5.1 is already 4 years old
5.1 Dec 2016 Dec 2021
Eventually this date will pass and we won't test against this version or fix bugs for it anymore.
Yes we are going to upgrade to 19.2 (maybe 20.1 if it comes out soon ) but wanted to do the ORDS upgrade first to test out the web services.