I have VCSA 7.0 running on my infrastructure. Esxi hosts are also running version 7.0 However I cannot enable FT on the VCSA VM itself. When I try to turn on a alert shows that FT cannot be enabled on VM which has CPU Hotplug enabled. So I turned down the vcsa and from the esxi unchecked CPU Hot-plug and reboot the VCSA. Now again trying to enable FT, the same warning is coming. Even I cannot power it down otherwise since this setting changes must be made on vcenter, then where will vcenter come if it is down already.
FT should not be enabled on the vCSA itself. That's why vCenter HA exists for this very purpose.
Do this procedure and check again:
Shutdown the vCenter
Connect to the ESXi host which the vCenter resides on.
Browse the datastore that the vCenter resides on.
Find VMX file of vCenter and edit it as below and save:
vcpu.hotadd = "FALSE"
vcpu.hotremove = "FALSE"
Also please noted: FT can only be used to protect vCenter Server for the tiny and small deployment type.