Even identical twins can be told apart by a blood sample. Something to do with their antibody profile.
I could see that possibly being so. But I'd like to see a study on it. A lot of DNA tests are kept pretty simple. Not even a full DNA comparison, usually just comparing a set number of areas within the DNA profile.
I don't know much about it, but have seen the interesting things occurring due to chimerism (two sets of DNA in the same person in different parts of the body). Not seen much about identical twins other than on crime dramas in such regards.
If you've got a link for the antibodies I'd be very keen to read about it.