I know many of the 'pure' ethnic Germans welcomed the invasion and were given German citizenship; but considering how intertwined both peoples were in Western Poland (Silesia in particular), were the people of mixed German/Polish blood counted as German?
Furthermore, was there a standard akin to measuring for Jewish facial features to judge who was Germanic enough and who was too Polish or slavic for the lebensraum expulsions or during the ethnic cleansings?
Were there any considerations towards this issue within the Generalplan Ost?
The answer depended upon the Gauleiter. In the most infamous example, Albert Forster, the Gauleiter of Danzig-West Prussia, received Hitler's infamous instruction to "Germanize" his territory at the same time as his rival Arthur Greiser, Gauleiter of Wartheland. This was part of the Heim ins Reich (Home to the Reich) policy.
Since Hitler said he "would ask no questions about their methods", Forster simply "Germanized" those Poles who claimed to have German blood without a measurable 'standard'. Greiser, on the other hand, did not, and complained to Himmler that Forster was not implementing Hitler's direction. However, Forster knew that Hitler would allow his subordinates to fight out the matter among themselves, and he was right. Hitler did not intervene, and the Gauleiter was allowed to run his territory as he saw fit, which was traditional in Nazi government.
Greiser, on the other hand, was more committed to a polenrein (Polish-free) Gau, and was in fact one of the architects of the Holocaust in Poland.
For more information:
http://ww2db.com/person_bio.php?person_id=612 (Forster)
http://www.holocaustresearchproject.org/othercamps/greiser.html (Greiser)