I'm working with Content Web Services on CS10, Service Pack, Update 11.
I have a category like so:
Category Name: "Varied Category", all attributes locked at 1, not required
Attribute 1:
Name: "A Date"
Type: Date Field
Attribute 2:
Name: "An Integer"
Type: Integer field
Attribute 3:
Name: "A Text Field"
Type: Text Field
Perform a call similar to:
DocumentManagement.AttributeGroup _attribGroups = DocumentManagement.GetCategoryTemplate( ref _otauth, category.DataID);
Inspect _attribGroups and you will find that for the Values field, The DateTimeValue and the IntegerValue DataValues both have default Values fields created, but string types are null. Easiest to see in a picture:
