Currently, there is no option to wait for a valid license (either SLM or key-based) when utilizing the Jenkins TestComplete support plug-in. Without this feature, parallel tests can fail if there is no license available during the time of the test. It would be nice is there was a switch to wait for a valid license prior to executing the TestComplete/TestExecute test.
There are workarounds that help to some extent; however, they are not complete and do have issues. For SLM licenses, utilizing the Lockable Resources plugin helps, but this only works for resources that are included under the scope of Jenkins and those Jenkins tests accessing the locks. Furthermore, tests can still fail due to a slow release of the license.