"Anyway, I'll start flying internationally by the end of the year (at least once every two months) and mostly to Poland (we just opened an office in there) so I'll be mostly on KLM and NW. I've not checked yet If CO has codeshare on AMS-WAW with KLM but I hope it does. "

As long as your flight is ticketed as NW flights and not KL, and make sure to keep copies of your ticket and boarding pass, because you will have to probably mail it in - then you should have no problems on having it count towards your elite miles.