Good morning,
Quoting from that same documentation link:
Note
VLAN
225 (10.90.14.1) exists as a Layer 3 interface on the MSFC to route
Client traffic to the CSM-S. VLAN 14 (172.16.1.254) is also configured
on the MSFC to allow administrative traffic to be routed to the SSL
daughter card. VLAN 14 (172.16.14.1) is configured on the CSM-S to send
and received SSL traffic to/from the SSL daughter card. VLAN 6
(192.168.6.1) exists only as a VLAN in the VLAN database and as CSM-S
and SSL daughter card VLANs, but it does not have corresponding Layer 3
interfaces on the MSFC.
As you can see, the only reason why the SSL vlan is configured on the MSFC is for management purposes. It is not required for the correct operation of the CSM-S. In your case, you could just configure this vlan as a L2 one on the switch so that, from the IP perspective it's still behind the FW.
Regards
Daniel