As per platform support guide 12.2.1 is supported in Pega 7.3.1. There are conflicting responses in community on if it higher versions that are not in the guide are supported.
https://collaborate.pega.com/question/weblogic-compatibility-pega-73 -Not recommended
https://collaborate.pega.com/question/weblogic-12213-supported-prpc-722 - Supported
Can Pega support an upgrade to weblogic 12.2.1.4? Is it recommeded?