Since these are "vintage" source codes, there should be no concern regarding possible hacks. Emulators for the original Xbox already exist and are said to already be using the leaked codes, but still cannot provide complete compatibility with today's PC systems. As for the impact of the Windows NT 3.5 source code leak, there probably are very few systems still running this OS and these are most likely not connected to any relevant data center.
https://www.notebookcheck.net/Original-Xbox-and-Windows-NT-3-5-source-codes-leak-online.466221.0.html