While it is true that SSL-VPN is not exposed directly within vCloud director you can still configure it manually through the vShield appliance (Network Virtualization tab in vCenter). Everything works just fine even after redeploying the EDGE part in vCloud, I can confirm this specifically for vCloud Director v5.1.0.810718 with vShield v5.1.2-943471.
So far nothing gets overwritten but it may not be the case with different versions of vCloud + vShield (I haven't found any notes / remarks within the official docs). If you have any doubts around such implementation of SSL-VPN then I strongly suggest you to test it out yourself and see how it would work for you. Let us know your experience as well as the details of your implementation.