SPNego for multiple domains/forest

Hi,

I have more than 20 domains in my system.

In the current state, if I have a user 'ocohen' in domain X and another 'ocohen' in domain Y only one of the users can log to the portal because the samaccountname is not unique.

A possible solutions are change user name for the duplicates or change the mapping attribute from samaccountname to something like employeeID, or email (unique attribute in Active Directory).

My question is: if I'll use SPNego, will the duplicate users can log on without a problem?

My portal is EP6 SP16 and I'm aware that configuring it with multiple domains/forest will require me to upgrade it to at least SP18.

Thanks,

Omri