If you're looking for a wireless adapter, it's net.wlan.devices, not net.vlan.devices. When net.wlan.devices is empty it just means that FreeBSD doesn't recognize any wireless adapters. That doesn't necessarily indicate the machine doesn't have any, it could be a card that requires a specific module to be loaded before it's recognized. Or it's a completely unsupported wireless adapter.
The best way to see what's actually in the machine is by using pciconf -lv. Hardware should always show up, even if FreeBSD itself doesn't support it.