The vast majority of narco crime in NL is done by ethnic Dutch people. Sure, there's other ethnicities too. Like most crime, generally it's a pretty representative mix of the poorer classes.

Immigration causes all kinds of things, good and bad, but increased drug crime isn't really on the list so far.

Source: I live in the south of NL (narco hotspot) and I read the local newspaper. Majority of drug criminals caught have Dutch names. I'm sure there's better stats somewhere but can't be arsed.