As far as I know SSL in SPAN mode is supported, that's why it worked in your customer!
Limitations are related with hardware in first place: SSL decryption is not supported by I‑1200, I‑1400, M‑1250, M‑1450, and N‑series Sensors. In second hand these are SSL functionalities that are not supported:
• iPlanet Web servers
• Diffie‑Hellman ciphers (McAfee recommends that you disable acceptance of Diffie‑Hellman requests
on the SSL Web server to ensure that Network Security Platform is able to decrypt the traffic)
• Compression in the SSL records (a negotiable option in SSLv3 and TLS)
• PCT (Microsoft's extension to SSLv2)
For further details please check IPS Administration Guide - Page 540.