  The $O(\alpha)$ electromagnetic radiative corrections to the $B^- \rightarrow
V^0 \ell^- \bar{\nu}_{\ell}$ ($V$ is a vector meson and $\ell$ a charged
lepton) decay rates are evaluated using the cutoff method to regularize virtual
corrections and incorporating intermediate resonance states in the real-photon
amplitude to extend the region of validity of the soft-photon approximation.
The electromagnetic and weak form factors of hadrons are assumed to vary
smoothly over the energies of virtual and real photons under consideration. The
cutoff dependence of radiative corrections upon the scale $\Lambda$ that
separates the long- and short-distance regimes is found to be mild and is
considered as an uncertainty of the calculation. Owing to partial cancellations
of electromagnetic corrections evaluated over the three- and four-body regions
of phase space, the photon-inclusive corrected rates are found to be dominated
by the short-distance contribution. These corrections will be relevant for a
precise determination of the $b$ quark mixing angles by testing isospin
symmetry when measurements of semileptonic rates of charged and neutral $B$
mesons at the few percent level become available. For completeness, we also
provide numerical values of radiative corrections in the three-body region of
the Dalitz plot distributions of these decays.
