Use DRS affinity rules to control where the VM lives, this should limit the "what host is vCenter on" game in case of a true disaster/total environment outage. Otherwise, last I checked dvSwitching only requires vCenter to make changes, not to run, so vCenter being down is a management issue not a functional issue.
As a consultant I have several environments with vCenter on a VM, so far minimal issues. In many cases, any issues are offset by avoiding the cost of hardware, licensing and maintenance on a dedicated physical host.
The few environments still using a physical vCenter are using it as a secondary role on the backup server, since connecting to tape drives from a VM is still a problem.