The Jenkins Release Plugin (https://wiki.jenkins-ci.org/display/JENKINS/Release+Plugin) does not honor the Global MAVEN_OPTS specified in the 'Manage Jenkins -> Configure System' section.

As a work-around, I have had to add add the MAVEN_OPTS to the Goals of the release build:
--batch-mode release:prepare -DreleaseVersion=${RELEASE_VERSION} -DdevelopmentVersion=${DEVELOPMENT_VERSION} -Djavax.net.ssl.trustStore="/path/to/jenkins/truststore.jks"