BigIP in multiple vlans: Possible security issue

Hello, i have a question because of a possible security issue. A BigIP with two interfaces is connected to an internal an external firewall. In the same internal and external VLANs are multiple application server. The default gateway of these app server is the internal or external firewall. If i change the DG of the app server (because of a configuration mistake or consciously), so the new DG is the internal or external ip of BigIP. What happens with the whole traffic (not only loadbalanced traffic) ? Is all traffic going through BigIP and is not restricted and controlled by the firewalls ? Hope it is clear, what i want to describe.