Wis. Stat. § 879.11: Notice requirement satisfied by appearance.

An appearance by a person who is not a minor or an individual adjudicated incompetent is equivalent to timely service of notice upon the person. An appearance by a guardian of the estate is equivalent to timely service of notice upon the guardian and upon the guardian’s ward. An appearance by a guardian ad litem is equivalent to timely service of notice upon the guardian ad litem and except at a hearing to prove a will or for administration is equivalent to timely service of notice upon those whom the guardian ad litem represents. An appearance by an attorney, or an attorney-in-fact, for a person in the military service is equivalent to timely service of notice upon the attorney or attorney-in-fact but does not satisfy a requirement for notice to the person in the military service.