According to the latest APM 10.5 Wiki, the CA APM for Web Servers is currently not delivered as an install-able service for Unix/Linux. The startup can only be done via the manual script WebServerMonitor.sh.
Having said that, you can achieve the same objective by creating your own entries in the AIX RC directories to enable auto start of the WebServerMonitor.sh.
Please refer to following IBM tech note for more details on how to do so:
Starting and Stopping Software via RC Directories