There may be a few things going on here, and the answer depends upon what you're trying to accomplish. For a flow like this:
Client --> Router --> BigIP Virtual Server
The BigIP itself actually doesn't need a route at all: it has a feature called 'auto lasthop', which simply means it keeps track of the last MAC address that sent the flow to the Virtual Serer, and it'll send it back to that MAC by default.
So to try and answer your question I'll make two assumptions you are either wanting to do:
1) Source traffic from the BigIP itself (for DNS, NTP, etc for example)
2) Handle traffic sourced from pool members behind the BigIP.
3) or, more likely, both #1 and #2 above :)
The flow now looks like:
Client --> Router --> BigIP Virtual Server --> Pool Members
Basically, if you've got a default route set up on the BigIP (using your #1 method above) and your pool members point to the BigIP floating IP address as their default route, flows will behave as you expect. If your pool members point to another router for their default gateway, you'll need to enable SNAT on your virtual server so the pool members will send the traffic back to the BigIP as opposed to their default gateway.
There are a few other, more advanced, configurations available (multiple gateways, multiple server vlans behind BigIP, etc.), but it sounds like you're on the right track.
Btw, tcpdump is your friend :).
For more questions I'd check F5 DevCentral out; chances are good your exact question has been answered there already.