This answer cleared my confusion. ll study materials won't tell you which one to configure first --UCS blades and vcenter...
For example:
I have 9 hosts on cisco UCS blades and 50 virtual machine servers sit on these 9 hosts.
I need to install ESXi 5.1 on these hosts separately or install ESXi 5.1 on a single console after configure UCS to make it as a single data center?