Hello Bob,
I know that, at least with looking up and adding AD users in the Workflow windows in GP, when an AD user doesn't have a Display Name setup in the AD user account properties, the domain name will show up in People & Groups, but when clicking OK to add it to Workflow, it doesn't show up in the GP window, similar to what you're seeing.
I don't know if it is the same for the lookup in the User Setup window or not, but I'd make sure these AD users you're attempting to add into GP have a display name specified in their AD user properties and if not, add that, then launch GP and test again.
Usually, other than this display name issue we've seen with Workflow, it's all-or-nothing, meaning that either you see the AD name and can add it into GP or you don't see the name at all.
If the users are in a different domain than the SQL and GP applications, you'd need a full, two-way trust between the two domains and then the account you're logged onto the machine as (your Windows account, not GP login) would need permissions to query, in this case, the CORP domain and find those AD users to add into GP.
As you're seeing the users, it seems you have permissions enough to query the domain where the users exist, but maybe not enough permissions or not a two-way, full trust between domains to add the users into applications on the COMPANY domain?
Another test you could try, in SQL Server Mgmt Studio, under Security > Logins, can you add these domain users into SQL? If not, then it may be an issue trying to add those users onto an application on a domain different than that of where the users exist, which would seem to point to an issue with the two domains not fully trusting each other.
I'd start with that and see what you find, let us know.
Thanks,
