  We perform a sensitivity study of dark energy constraints from galaxy cluster
surveys to uncertainties in the halo mass function, bias and the
mass-observable relation. For a set of idealized surveys, we evaluate
cosmological constraints as priors on sixteen nuisance parameters in the halo
modeling are varied. We find that surveys with a higher mass limit are more
sensitive to mass-observable uncertainties while surveys with low mass limits
that probe more of the mass function shape and evolution are more sensitive to
mass function errors. We examine the correlations among nuisance and
cosmological parameters. Mass function parameters are strongly positively
(negatively) correlated with Omega_DE (w). For the mass-observable parameters,
Omega_DE is most sensitive to the normalization and its redshift evolution
while w is more sensitive to redshift evolution in the variance. While survey
performance is limited mainly by mass-observable uncertainties, the current
level of mass function error is responsible for up to a factor of two
degradation in ideal cosmological constraints. For surveys that probe to low
masses (10^13.5 h^-1 M_sun), even percent-level constraints on model nuisance
parameters result in a degradation of ~ sqrt{2} (2) on Omega_DE (w) relative to
perfect knowledge.
