It is bit surprising that they do not offer Java UBI image, considering that RH is one of the biggest Java vendors. Instead they are offering dotnet images of all things.
When you consider that you realize that adding a Java UBI image would just set them up for a fight with Oracle and delay their ability to get moving with UBI.
.. it doesn't seem they're hugely afraid of openjdk
Additionally IBM, Red-Hat and Oracle, collaborate on OpenJDK development and are the few set of companies that actually contribute new language features, with Oracle still having like 90% of contributions.
$ docker run --rm registry.access.redhat.com/ubi8/ubi yum search openjdk
java-11-openjdk.x86_64 : OpenJDK Runtime Environment 11
java-1.8.0-openjdk.x86_64 : OpenJDK Runtime Environment 8
java-11-openjdk-devel.x86_64 : OpenJDK Development Environment 11
java-1.8.0-openjdk-devel.x86_64 : OpenJDK Development Environment 8