I'm guessing this is not a coincidence. Is there an official source that confirms the naming of his Zootopia character is related to his Frozen character?
Alan Tudyk confirms this
In a red carpet interview for Zootopia he addresses this directly.
Well, I have convinced Disney that I should be in everyone of their animated movies after Wreck-It Ralph and I've been doing a fairly good job of that, yeah. So in Frozen I was the Duke of Weselton and so in this movie I'm Duke Weaselton, because in Frozen I was always saying, everybody called him the Duke of Weselton, "he's Wesel from Weselton", and so the Duke Weselton, he's way up here so he's actually the Duke of Weselton, so he actually exists now.