Have you enabled Source Address Translation: Automap on the Virtual Server? (It may show as SNAT in some versions).
You can also check the Virtual Server and Pool statistics to see if traffic is going in and out. You can find those on:
Local Traffic > Virtual Servers > Statistics
Local Traffic > Pools > Statistics
You can also run a tcpdump from the bash command line, for example:
tcpdump -nni 0.0
which will show you the traffic that's going through the traffic interfaces.
Other examples:
tcpdump -nni vlan_name
tcpdump -nni 0.0 host 192.168.x.x
You can see more examples in SOL411