Modification is the whole point of open source: "Unless you want to modify Windows, the closeness does not impact you". If you want to learn about how NetBSD looks at things, there is this page:

https://netbsd.org/about/redistribution.html

As for being compatible. Yes, FSF considers anything permissive to be compatible with their family of licenses. However, it is a one-way relationship in that permissive code can be freely used by GPL projects, but not the other way around as using GPL code would impose further restrictions compared to a permissive license.