I think it unlikely they'd be called Dukes of Brabant even if it forms part of this Zeelandic Normandy. The title is essentially the merging of Landgrave of Brabant with Duke of Lothier/Nether-Lorraine.Having Vikings raid down the Rhine would be fairly likely, IMO. Especially if Cologne is a major city.
In which case, having a Normandy analogue in the Zeeland-Brabant-South Holland area might be plausible. Maybe they get installed first as counts of Breda, then later as Dukes of Brabant?