Spy probably sends secret checks to Scout's mom after he met her (since we dont know if she ever was employed, 8 kids must not leave a lot of time for work and cost a fortune in time and patience)
BUT
We dont know when Spy and Scout's mom strated dating, and how long in the relationship Scout came around or how many brothers there was around already
Also i imagine Spy knowing full well the names and addresses of Scout's stepdads, but never done anything unless Scout's mom asked him to
Maybe he disguised himself as an uncle to come visiting from times to times ? His spytech would be handy to do Santa stuff
Dammit I think i established Santa might use spy technology in the TF2verse