... , is it required to update vcenter first?
Yes, for some of the updates, it's required to update vCenter first, see VMware Product Interoperability Matrices
Btw. how do you patch the hosts? In case you do this from the command line using esxcli, there's no need to install the updates one after the other. Assuming that you have supported hardware, you can directly install the latest patch bundle. Note that there might be restrictions regarding the upgrade, if you are using a vendor/OEM ESXi installation.
André