As DrDu already wrote MOs are approximations of solutions of the Schrödinger Equation. Hybridization is something different. Hybrid orbitals are formed by mixing of orbitals. If the original orbitals are approximations than the resulting hybrid orbital is an approximation too. But if the original orbitals would be exact solutions than the hybrid orbital would be an exact solution too because linear combinations of solutions of a differential equation are also solutions of this differential equation. Therefore hybrid orbitals are as "real" as any other orbital.