Can aroma therapy be used for migraines?

Yes. Migraines are a result of autonomic nervous system confusion and can usually be treated by nutritional therapy by correcting diet and adding supplements. Medication is often affective but does not address the cause.
For some, yes. Applying dilute peppermint oil to the forehead and temples may help -- as long as you aren't overly sensitive or allergic to this oil. Non-aromatherapy herbals such as feverfew and butterbur can be very helpful also.
Yes. Yes with certain fragrances like lavender and vanilla which can relax you but certain odors can certainly exacerbate migraine headaches as well it depends upon the person esp strong solvents or chemicals.