We consider possible mixing of electromagnetic and gravitational shock waves,
in the Planckian energy scattering of point particles in Minkowski space. By
boosting a Reissner-Nordstr\"om black hole solution to the velocity of light,
it is shown that no mixing of shock waves takes place for arbitrary finite
charge carried by the black hole. However, a similar boosting procedure for a
charged black hole solution in dilaton gravity yields some mixing : the wave
function of even a neutral test particle, acquires a small additional phase
factor depending on the dilatonic black hole charge. Possible implications for
poles in the amplitudes for the dilaton gravity case are discussed.Comment: 11 pages, revtex file, no figure