As I mentioned before, even if you're not a DT member, you still have the ability (and should use it) to provide trust feedback, just like any other forum member. For now, your feedback will be displayed as "Untrusted feedback" on the user's profile. However, if you use your feedback the right manner, following norms and best practices, other members will take notice and may consider including you in their trust lists. This is how you can eventually earn the status of DT. On the other hand, if you choose not to provide any feedback, there's no reason for people to consider promoting you to DT, since no one can predict if you'll use your powers for the betterment of the community or not.