Will my dark, velvety diabetes type 2 spots go away if I lose weight? If not, what can I do?

Most likely yet. Acanthosis nigricans, the dark spots you're explaining in most instances is a sign of Insulin resistance and high blood sugar in obese and diabetic individuals and with weight loss and control of blood sugar goes away. If it's due to another condition like growth hormone intake, birth control pill or genetics, then unless the condition is treated, it won't go away, i.e. In genetic cases it won't.