Hello there.
I always thought that vpxuser is created on ESXi during the process of attaching it to vCenter. Hoewever I figured out that this account exists on ESXi even if the host is not managed by vCenter and never was (I dont know where i`ve read the info that vpxuser exists only if the host is managed by vC, there is no such info here vSphere 5.5 Documentation Center). So my question is: what vpxuser need for in case of standalone ESXi? And could the modification of its permissions or password somehow affects the standalone host?