  In Ho\v{r}ava and Einstein-{\AE}ther theories of modified gravity, in spite
of the violation of Lorentz invariance, spherically-symmetric stationary black
hole solutions possess an inner universal horizon which separates field
configurations into two disconnected classes. We compute the late time
radiation emitted by a dispersive field propagating in such backgrounds. We fix
the initial conditions on stationary modes by considering a regular collapsing
geometry, and imposing that the state inside the infalling shell is vacuum. We
find that the mode pasting across the shell is adiabatic at late time (large
inside frequencies). This implies that large black holes emit a thermal flux
with a temperature fixed by the surface gravity of the Killing horizon. In
turn, this suggests that the universal horizon should play no role in the
thermodynamical properties of these black holes.
