Well, this is my setup that I have under testing and seems to work.
Physical Hardware:
Laptop with 1 Ethernet and 1 Wireless built in.
1 dir-825
1 dir-655
1 dwa-160 (usb 2.4/5Ghz card)
Siemens Gateway
I have the Seimens gateway outward facing as it is being used as the ADSL modem > dir-825 as access point > dwa-160 > laptop > ethernet > dir-655 as second access point.
Stupidly complex setup but all i have is a laptop which I use for everything and the dir 655 is only in the equation to test how pfsense works as a NAC/router and AP.
As for software typology, I have pfSense as a guest OS inside VMWare 7. (versioning doesn't matter, I originally intended to try and figure out how I could fit esxi into the equation to eliminate all hardware routers and strictly have everything running as softawre and virtualised). Anyway, pfSense as a VM only has two Virtual adapters. The WAN and LAN (for now). On Windows 7, I had VMware create only 1 Vmnet adapter that I will be using.
In VMware (not pfSense webgui), I bridged what would be pfSense's WAN interface to my dwa-160 which is connected to the DIR-825. So now pfSense connects directly to my physical network and obtains the physical internal network ip address of 192.168.0.xxx
I set vmware to also bridge what would be pfSenses LAN interface to my physical LAN adapter. I put the ethernet cable into anything but the WAN port of the dir-655 (since i am still double nated this way) after turning off DHCP in the router. With both virtual adapters bridged to physical adapters, I am able to test pfSense outside the virtual environment. IE: how physical computers will be affected by pfSense. I did however have to set static IP address for the LAN adapter within pfSenses network segment.
Now, to test the network as an access point, I just connect my built in wifi adapter (not the dwa-160, remember I listed I had 2 wifi cards) to the dir-655 which is now successfully hardwired to the laptop and see if the wifi adapter gets an IP address from pfSense, which is a success. However I can't test against pfSenses functionality because Win7 will be using my dwa-160 as it's internet connection and any changes to it will affect network connectivity with the AP and pfSense. For THAT, I load up Win7 in VMware and connect the laptops built in Wifi card directly to it. Once the Virutal Win7 see's the card as a real device, I then do the same, connect it to the dir-655. I get an IP address from pfSense, great, AND I get internet as expected. Traffic is flowing through pfSense as it should and so is the L7 and other QoS rules and the portal. I am sure that it will communicate just fine with the radius server as well.
So in terms of a wireless router hardwired to the machine that is running pfsense as a vm and having it act as an AP, yes it's do-able.
If your method of connectivity includes a modem that has wireless capabilities ie:Gateway, then the method I described above will work fine. Your physical machine will not be affected by pfSense but you will should still maintain access to the webconf without having to load up a seperate VM.
If you want to have VitualBox use a wifi usb as a passthrough device, you will have to check on the HCL if the wifi chipset is a supported device and if OpenSolaris supports it, otherwise VirtualBox won't detect it. My guess is that you may have a lot of device hacking and scripting that you may have to play with.