  We study, at zero temperature, the dynamics of a single electron in a
Holstein model augmented by site-diagonal, binary-alloy type disorder. The
average over the phonon vacuum and the alloy configurations is performed within
a generalized dynamical coherent potential approximation. We present numerical
results for a Bethe lattice with infinite coordination number. In particular,
we investigate, in the intermediate electron-phonon coupling regime, the
spectral and diffusion properties in the vicinity of the high-energy edge of
the lowest polaronic subband. To characterize the diffusion properties, we
define a spectrally resolved delocalization time, which is, for a given energy,
the characteristic time scale on which the electron leaves a given site. We
find the delocalization times substantially enhanced for states with a large
phonon content, i.e., in the absence (presence) of alloy-type disorder at the
high-energy edge(s) of the polaronic subband (mini-subbands). According to
their delocalization times, we discriminate between ``fast''
quasi-particle-like and ``sluggish'' defect-like polaron states and
qualitatively address the issue of trapping of an electronic carrier.
