(my apologies for diverging into VMware specific terminology for those of you deploying BIG-IP VE on Hyper-V or Xen):
The long answer:
VLAN Groups are a supported method of bridging a layer 3 topology over at least two layer 2 topologies, or VLANs. Deploying a VLAN Group configuration usually requires adjusting the configuration of the hypervisors vSwitch to accept multiple MAC addresses from a single virtual port. This is often not desirable for all hosts on a VLAN, and in fact overlapping portgroups can be combined on the same vSwitch, where one has forged MAC addressing enabled and the other is left to the stock unimac port settings.
That being said, usually, the hypervisor's switch infrastructure can be utilized for bridging. This generally involves configuring multiple physical interfaces into a single vSwitch, and then a single virtual NIC of the BIG-IP VE is connected to this vSwitch.