There are many reactions that take place when you dissolve Ca(OH)2, but in the end what matters when calculating pH is _measured_ values of Ksp and/or Kb - they typically take everything into account. That's because we don't measure these values directly, we calculate them from measured equilibrium concentrations of ions involved, and they depend on all equilibria involved.
Sometimes it means the result is only approximate, but for most calculations it doesn't matter, there are many more sources of uncertainty, most of the more important.