Almost 2 years back, I wrote that ESXi 4.1 supports USB pass through:
Recently I needed serial pass through as well, and surprise surprise, serial port pass through too was introduced with ESXi 4.1 as Vlatan Seget posted about a year ago:
in ESXi 4.1 since with this release of VMware Hypervizor now you have the possibility to attach and use the Serial port of the physical host.
Even better: it still works in ESXi 5 (:
–jeroen
via: Serial Port handling in ESXi 4.1 | ESX Virtualization.
The Wiert Corner - irregular stream of stuff 