Could DNA evidence be used as a second witness?
Not among Jehovah's Witnesses. No, they require 2 eyewitnesses, sometimes that means in addition to the victim, sometimes it doesn't. Depends on the elder body. Which is why you'll see entire congregations rally to support a convicted rapist, pedophile, etc. because there were not 2 eyewitnesses. If DNA, or the state by virtue of a conviction, counted, you would not see the congregation giving support.