Don't ask don't tell will have no impact one way or another regarding anti-gay violence in the military. Generally speaking, the military is made up of macho type men who do not support homosexuality. There will always be a percentage of those men whom believe violence is acceptable behavior. Making rules or laws are not going to change that.
Make no mistake, the ending of "don't ask don't tell" helped the American military greatly. It reduced the amount of discharges due to homosexual conduct, ending a brain drain of talented individuals that we were lucky to have in our armed forces. However, studies do not appear to back up that this has had any affect on anti gay violence in the military or elsewhere. People who attack other people on a characteristic such as sexuality are likely mentally ill, and are going to need more than a policy change to fix whatever is broken within them.