ESXi does not support Linux file systems and therefore does not know them (see: Types of Datastores ).
You can only connect USB hard drives with a Ext3 filesystem to ESXi and then pass them as USB pass-through devices to virtual machines, but you can't connect it as a local datastore to copy files on ESXi level.
I know that the ESX hypervisor is a cut down version of linux,
Basically, ESXi is no longer Linux but it is now its own operating system, which only has similarities with Linux.
I was fairly certain that I read it somewhere so I exercised my Google fu and found the article...
Is says mount is used as follows:
mount /dev/[device_name] /mnt/usb -t [filesystem_type]
It was updated in 2017, but was originally written in 2010 based on the comments, so what may have once been possible is no more.
That blog was written for ESX not ESXi.
Nowadays ESXi can only mount VMFS and FAT 16 and there is no mount command available.