I have created a dynamic typed list. I have added the following relations and predicate expression:

ResultsetFields fields = CustomResultsetFields.AuthorContentList();
//.... other code here
filter.Relations.Add(UsersEntity.Relations.CmsContentEntityUsingByline);
filter.Relations.Add(CmsContentEntity.Relations.CmsContentNotesEntityUsingContentID);
filter.PredicateExpression.Add(PredicateFactory.CompareValue(UsersFieldIndex.UserID,ComparisonOperator.Equal, userId));

Users.UserId is not in the ResultsetFields. When using a dynamic typed list, must a filter field be included in the select list?

No, fields in filters and sorters just have to be in hte entities in the relations in the relation collection