VUM uses its own database and it needs te be an Oracle or SQL database. You cannot use the VCSA builtin database.
The steps to install VUM are described in the vSphere 6 documentation and specifically in the section Installing and Administering VMware vSphere Update Manager, vSphere 6.0 Documentation Center
On that Windows 2007 you wither use a SQL Express, or a SQL Server to install that VUM. Or if you have any Oracle DB that you could connect to.
But the easy way should have a SQL Express on that Windows 2008.
More information here: https://kb.vmware.com/kb/2142791
I believe this is what your requirement.
You have VCSA 6.0U2, SQL 2012 DB system, you want to install VUM connecting DB which is on other system.
1. Create 32-bit DSN on VUM system pointing to the SQL DB system using SQL native client.
2. Install VUM using DSN created above
And refer to "Preparing the Update Manager Database" section. Its easy to follow.