Does the Oberth effect motivate complementing ion electric propulsion with chemical rocketry?

The solar electric ion propulsion engine of the Dawn spacecraft to Vesta and Ceres used Mars for gravity assist. Would it be gainful to complement an ion engine with a high thrust (solid) chemical rocket to fire only during such a gravity assist in order to make maximum use of the Oberth effect? Or can it be indicated that the burden of launching and carrying its mass would be difficult to make up for in that way?

A mass-conscious mission designer is always aware of solids' low specific impulse, yet may use them for their reliability in single-burn maneuvers. Powered gravity assists are mostly done in several burns (Venus-Earth-Earth, for instance), and require very high precision as far as burn $\Delta V$ is concerned. It may be also desirable to re-program burn length in-flight, which is not possible with solids. Hypergolic-based thrusters are much more convenient, well-tested, and flexible.