Are black holes considered part of baryonic content of universe? Are black holes (like those detected by LIGO, for instance) part of baryonic content of universe or part of dark matter? Why?
Black holes formed after the epoch of primordial nucleoynthesis would be part of the baryonic matter, since they would be mostly formed of baryons. It is possible or even probable that every black hole must contain some non-baryonic matter too, since there is nothing to prevent it being accreted, in small amounts, directly into black holes. However, the cross-section for that is very small because dark matter falling towards a black hole has no means to lose angular momentum. Unless there is almost a direct hit within the photon sphere then it won't be accreted. Normal matter can form an accretion disc and lose energy and angular momentum through viscosity, radiation and other processes.
Since the fraction of dark matter that is in black holes formed since the big bang is negligible, then the approximation that their mass consists only of baryons is hardly a big deal when it comes to doing the mass budget for the universe.
Primordial black holes on the other hand, that were already present at the epoch of cosmological nucleoynthesis, would not be counted as baryonic matter and it would be possible that they could contribute significantly to the required non-baryonic component, if they exist.
Could there be dark matter black holes? is essential reading.