There are a number of options available (vCenter, Syslog, SNMP, Agents (for example, HP/Dell), etc.) ... as you mention vCenter I assume you are licenced and use this already and should take advantage of all the alarm definitions and triggers which you can use this to send email notifications, etc.
I think you first need to clarify what your monitoring requirements are what the monitoring team will do in the case of getting alerted of any problems. Are you just monitoring the hosts or VM's as well? I am going to assume just the hosts, so here are some examples of what you can monitor using vCenter;
- Host is unavailable, disconnected, performance thresholds
- Storage paths, performance
- Network ulpinks degraded, redundancy, etc.
The possibilities are endless, so first be clear on your requirements and then set out satisfy all of them.