The Dutch, Belgians, Scots, Norwegians and Icelanders surely had quite limited genetic exchange with Slavic people as they are not direct neighbours with any of them. Anyway I seriously doubt than cross-cultural intermarriages between regions that never not belonged to the same country would account for more than a tiny fraction (<1%) of all DNA in a population. Political borders and language barriers are strong deterrents to intermarriages. If that did not convince you, just check the facts: over 95% of R1a in Germanic countries in of non-Slavic origin (subclades L664 and Z284), and the 5% that could be Slavic is found almost exclusively in areas that were part of the Corded ware culture or the Holy Roman Empire (most Germany), or Austria because of its own empire comprising many Slavic regions.