When attempting to manually import Release Automation action packs, it appears to complete successfully but the actions aren't available for use in the Designer.
Additionally, the problematic action pack jar file is not located in <RA_HOME>/actionslib on the management server. However it is located in <RA_HOME>/uploadActions on the management server.
This particular problem was caused by the RA repository being unavailable while the action pack installation occurred. Once the RA repository is brought back online, subsequent action pack installations will work properly.