Depends on the genetics of the fish. A DT with only 2 ray splits will throw VT when mixed with an HM. Always go by ray splits first to determine if your DT comes from VT lines or HM/Delta lines.
A DT (with more than 2 branches) mixed with an HM that carries DT (which may not always be expressed in the dorsal) will give you some DT in the original spawn.
A DT crossed with an HM that does not carry DT (getting harder and harder to find these days) will give you the mix Mr. V posted.