5 months is a long time to wait for a reply, but I come bearing good news. :-) I set up a ClearOS host with a OpenWrt guest using VMWare and USB wifi, and it is working perfectly.
Some details:
ClearOS Enterprise 5.2 as router & file server. ClearOS is derived from Red Hat.
VMWare player 4.0.1
Backfire 10.03.1-rc6 running bridged AP mode in a VM
Rosewill RNX-EasyN1 USB wifi adapter (Ralink RT3070), passed through to VM
If you care for more info, see my blog @ http://macbruins.wordpress.com
I also tried a TP-Link TL-WN722N (Atheros AR9271). It worked fine until the VM was rebooted. If I re-booted the host and VM together, no problem. If I powered off VM, unplugged adapter and plugged it back in, and then powered on VM, no problem. But if I rebooted jus the VM, the adapter would stop working.
I couldn't get VirtualBox to work at all. OpenWrt couldn't download firmware to the TP-Link through VirtualBox's USB pass-through. OpenWrt could initialize the Rosewill adapter working though VirtualBox, but no device could connect.
William