  One way to induce insulator to metal transitions in the spin-orbit Mott
insulator Sr2IrO4 is to substitute iridium with transition metals (Ru, Rh).
However, this creates intriguing inhomogeneous metallic states, which cannot be
described by a simple doping effect. We detail the electronic structure of the
Ru-doped case with angle-resolved photoemission and show that, contrary to Rh,
it cannot be connected to the undoped case by a rigid shift. We further
identify bands below $E_F$ coexisting with the metallic ones that we assign to
non-bonding Ir sites. We rationalize the differences between Rh and Ru by a
different hybridization with oxygen, which mediates the coupling to Ir and
sensitively affects the effective doping. We argue that the spin-orbit coupling
does not control neither the charge transfer nor the transition threshold.
