Are resonance structures sp, sp2, sp3 hybridized?

There are two ways to determine that NO₃⁻ ion is sp² hybridized.

I. By the bonding of the central atom:
According to Valence Bond Theory, sp, sp² or sp³ orbitals make  bonds and the unhybridized p orbitals make  bonds.
In each of the resonance structures below, the central N atom forms 1 N=O double bonds (containing 1  bond and 1  bond) and 2 N-O single bonds (i.e. 2  bonds). To sum up, the central N atom forms 3  bonds and 1  bond. It can be deduced that the central N atom is sp² hybridized, where the 3 hybridized sp² orbitals form 3  bond and the unhybridized 2p orbital forms 1  bond.

II. By the shape of arrangement of electron pairs:
In each of the resonance structure below, the central N atom forms 1 N=O double bonds and 2 N-O single bonds. According to Valence Shell Electron Pair Repulsion (VSEPR) Theory, the 3 covalent bonds are arranged as trigonal planar. It can be deduced that the central N atom is sp² hybridized by the shape (trigonal planar) of arrangement of electron pairs.