We use the Hénon-Heiles system as a paradigmatic model for chaotic scattering to study the Lorentz factor effects on its transient chaotic dynamics. In particular, we focus on how time dilation occurs within the scattering region by measuring the time in a non-inertial clock comoving with the particle. We observe that the several events of time dilation that the particle undergoes exhibit sensitivity to initial conditions. However, the structure of the singularities appearing in the escape time function remains invariant under coordinate transformations. This occurs because the singularities are closely related to the chaotic saddle, which is a time measure independent set. Using a Cantor set approach, we show that the fractal dimension of the escape time function is relativistic invariant. Finally, we relate the fractality in phase space to the unpredictability of the particle final destination. In order to quantify this fractality, we compute the fractal dimensions of the escape time functions as measured with inertial and non-inertial clocks, by means of the uncertainty dimension algorithm. We conclude that, from a mathematical point of view, chaotic transient phenomena are equally predictable in the proper and the inertial reference frames and that transient chaos is coordinate invariant.