Sharepoint 2010 using Kerberos Authentication within the DMZ

I'm wondering if I'm barking up the wrong tree here.

Within this document http://support.f5.com/kb/en-us/products/big-ip_apm/manuals/product/apm-aaa-auth-config-11-3-0/3.html it mentions that the client becomes a member and connects to the domain. I'm not sure we want this in our setup.

Here is what we are trying to do...

An external contractor who's not on our domain browses to our external sharepoint site. (https://sharepoint-vip.domain.com) and enters their username, SecurID token code and domain credentials. From here we want the client to pass through directly to Sharepoint IIS Servers via SSO on the back end.

I'm wondering if my testing is not working because the test machine is not a member of the LABDMZ.DOMAIN.COM domain.