Tried doing hwclock set via cli, which is I am guessing the same as setting it in the vsphere client.
No, it's not the same. One is the physical hardware clock and one the clock the OS running on the hardware (ESXi) keeps on it's own.
If it doesn't work setting the hardware clock from within ESXi, then reboot the server, enter the BIOS and change the date/time settings there.