Hi @stsc!
The short version is that anything is possible when it comes to software/code re-use, licensing, etc. (half of the code running the internet is probably somewhere on a website that has overflowing stacks 
)
The catch comes at the time of support, upgrades, compatibility, and in the case that some entity is really successful at using unlicensed code - large lawsuits (i.e. Apple / Samsung.)
Overall these social and legal constructs keep those large-scale malicious attempts at bay, and without measurable impact on the business model.
Hopefully that helps!