I raised essentially this same question in an earlier thread:
the attempted rape of Nancy Ling Perry on Nov 12, 1973The earlier case was decades ago, so DNA testing wasn't involved, but to me it posed exactly the same ethical question: if evidence obtained during a rape (or attempted rape) investigation points to the victim being herself involved in serious, unrelated, crime, should that evidence be used or admissible?
Rereading that earlier thread, it seems to me that some people were being rather noncommittal, reluctant to fully come down on either side. It SHOULD be a difficult call to make, ethically speaking. Perry was probably involved in some way in the assassination of a respected Black community leader, Marcus Foster, but was herself a victim of an unrelated attempted rape. If evidence obtained in the rape investigation had pointed to Perry's involvement in the Foster murder, should she have been charged?
For minor crimes I would say really strongly that, no, the rape victim should be able to come forward and report the rape without being afraid of herself being charged with some minor crime. For extremely serious crimes--and the crime Perry was accused of was extremely serious--I'm not so sure.