Neil,
Can you confirm your ServerSSL setup? See ServerSSL Overview page, To troubleshoot have you tried using the default ServerSSL profile? As mentioned in the link above, when a serverssl profile is added the bigip is acting as a client and uploading a cert means the bigip presents this as a client certificate to the pool member. From your description i'm not sure this is what you are after.
If you want to validate the certificate from the pool member then in the Server Authentication settings part you can specific the domain name of the certificate expected.
Hope this helps,
N