I don't know, I think that IBM per se was really in a position to know how the census machines they had given to Germany were actually being used. Remember that this was before the days of satellite communication, and as part of their war strategy the British cut Germany's telegraph cables (just like they had in WWI) and intercepted packets of mail between the US and Germany whenever they could, and generally did a pretty good job of it[1]. I'm happy to believe that people who were nominally IBM employees were servicing the machines, but if IBM headquarters wasn't being told what was happening, and if the employees faced getting shot if they didn't do what they were told, I'm not sure how much you can say that IBM knew in any meaningful sense.

[1] This was a point of contention between the UK and US before the fall of France.