Technically its still an extract even in powdered form, its just that its large. Can you make a tincture out of the powder with vinegar? Absolutely. Medicinal potency of tinctures are more powerful than the powders because the extracts become finer.
Vinegar as a mentrum works quite well but is not as strong as grain alcohol. However, alcohol-based tinctures taste horrible. When making tinctures, its a constant balancing act between taste and strength.