Whether OpenSSL is used or not will depend on the cipher string in your SSL profiles. If you're using the DEFAULT or NATIVE strings or something else that only uses native ciphers then OpenSSL is NOT used and the Cavium offload card (and related proprietary SSL/TLS software) is. If you're using something else (a compat cipher) then OpenSSL is. A cipher string specifying any compat cipher, even if the rest are native, will result in OpenSSL being used. <
Find the definitive list here and modify your profiles accordingly: http://support.f5.com/kb/en-us/solutions/public/13000/100/sol13163.html.
Also remember that you'll get much better performance if you only use native ciphers.