Logistically think about an adoptee. They have a full fledged adoptive family line. They have a full fledged biological line, once they find it.
Having mirror trees is absolutely a Genealogical and adoptions search recommended standard way of listing the pedigree of adoptees. An industry standard.
The connection on WikiTree is actually to two different people with two different lines. One adopted and one biological. The biological line is the line which would have any DNA tests attached to it.