I can't find a solid answer anywhere. Can you just not do wireless interface specific stuff in a virtualized Backtrack? All it ever comes up with for network interfaces in backtrack is the ethernet port and the loopback.
Short answer: You can certainly do wireless specific things inside a VirtualBox VM, But probably not as easily as you would like.
Long answer: It requires quite a few hoops to jump through. You really need to read the section of the VBox manual for PCI Passthrough. In short, you need to meet these requirements to even try it:
This will present the physical PCI card to your guest, so you would install the native wireless driver (or use the version that ships with your distro) in your guest. There are also some limits placed on what other VBox features are (not) supported when running with PCI passthrough - again read and understand the relevant section from the manual for this feature.
Note: this is answered for VirtualBox 4.1.10 - past/future versions may be different