I have a Xen-based Centos 5.5 virtual machine running as a server - Apache, OpenSSH, MySQL, Tomcat, Nagios and ISC Bind. It is currently running both
hal-daemon. Are these needed or can I safely turn them off?
Well... you can turn them off if nothing needs them. Kill D-Bus, and if nothing rolls over or complains then you can kill hal as well. "And the like" isn't specific enough to give any sort of an answer.