live USB and VMware Player

Live usbs as you say are just iso images setup to boot from a usb stick (Mostly copied & the bootloader added.)
In short; you may as well just use an iso image to save the hassle. If you want to do it because you are short on space; copy the iso image to the usb stick and select the iso image on the mounted usb stick as the image.

If your usb stick supports floppy emulation then you can add it as a floppy device and it may work.

Using virtualbox it may be possible to add the usb stick as a virtual disc some how or something like this :
http://lawand.wordpress.com/2009/09/22/boot-virtualbox-guest-from-a-usb-device/
As noted here :
http://forums.virtualbox.org/viewtopic.php?p=14648&sid=4843b05853d30ed930fbfac38088f06e
the virtualbox developers can't provide usb booting in the virtualbox bios (Patents I guess.)

As far as vmware goes, maybe someone else knows? It's probably quite similar.