Liferay has chosen not to individually certify OpenJDK binaries. The compatibility of open source JDK binaries will depend on the Java Technical Compatibility Kit (TCK) certification of that binary. Meaning, if a JDK binary is Java TCK compliant or certified then that binary will be compatible for use with Liferay.
The Java TCK testing kit allows an organization to test their compiled Java binaries and ensure the binaries comply with the Java SE standards. If everything passes then the organization will indicate that their binaries are compliant or certified.
Oracle Open JDK