But the largest part of the over-the-range microwave load is not the fan, but the microwave. 422.16(B)(3) should apply, and posts no restrictions.
422.16(B)(4) only requires it if the fan is plug-and-cord connected. If the range hood is hardwired, the normal rules would apply.
I must admit, though, I'm stumped as to why a corded range hood would be required to have an individual branch circuit, it doesn't make sense...
