Yes, it is possible to have the servers not connected to the CSS itself. The important thing here is that depending on your desing this may cause an asymetric floe, since the server response will bypass the CSS.
If you are not doing source NATing on the CSS, then the server is seeing the real client?s IP as the source IP, so it will try to respond directly to the client and will do it thru the layer 2 switch.
Since the client sent a request to the VIP on the CSS, when sees the response from the server will drop the packets.
You can configure source NATing on the CSS to prevent this issue.
Configure a group and use add destination service to add the servers, like this
group test
vip address 192.168.1.1
add destination service server1
add destiantion service server2
active
If you do not want the source NATing option, you can configure the servers to point to the CSS as their default gateway, that should prevent the asymmetric flow as well.
Hope it helps!!