Yes, I was an unbeliever when I joined the military and afterwards I was concerned but came to the conclusion it was good to be in the military protecting family and country from the forces of evil who plainly declared "We will bury you".I think it is more along the lines of this: You do not walk after your own flesh as a believer. So why take an oath, or sign a contract that forces you to walk after the flesh of an unbeliever. This would rule out everything from marrying an unbeliever to joining the military or working under oath as the civil magistrate.
But bank loans to not require this. So you could proceed with a clear conscience in home buying or any other type of loan.