They're not part of Scandinavia, no, but geographically and economically Netherlands and Germany (at least the northern part close to Denmark) are also considered northern european (not to be confuse with The Nordics).
I never heard of Germany being Nordic country.
BeNeLUx and Germany is not a part of the Nordics.
"Nordic countries" is a very well defined group: Sweden, Finland, Norway, Denmark, and Iceland.
Germany and Netherlands may be in Western or Central Europe depending on definition, but I've never heard of them being grouped to "Nordic".