I am not very familiar with ACI, but the most straightforward answer to your main question is that you cannot assume that the structure is uncracked just because it is a shell - regardless of what an ACI chapter says about it. If you wish to prevent cracking, you must ensure that the cross-sectional stresses do not exceed the tensile strength of concrete; this can be achieved by limiting shell geometry (e.g., a dome with restrictions on width-to-height ratio) or by introducing prestressing. For a general shell (no axisymmetry, non-uniform load), ensuring an uncracked cross-section is very difficult.
Furthermore, I wish to emphasize that modeling a shell (or slab) with zero Poisson's ratio is incorrect, because a basic concept of shells and plates (2D objects) is that Poisson expansion is restricted, resulting in a higher stiffness than for a beam. Illustrating the relevance of Poisson's ratio for the isotropic case:
a beam: bending stiffness = EI = E*(b*h^3)/12
a plate: bending stiffness = D = E*t^3/(12*(1-v^2)) , where v = Poisson's ratio
The shell is simply a stiffer plate (initial curvature increases stiffness and capacity), and from the above two equations, a difference of (approximately, depending on material) 20% in stiffness - in favor of the plate - can be observed.
This advice applies to modelling with FEM or performing hand-calculations. You may, of course, calculate an extremely conservative deflection approximation by neglecting the shell stiffness and instead using a beam model, but this should be done using the internal forces received from elastic theory (which includes non-zero Poisson's ratio), because elastic theory is what correctly predicts the distribution of internal forces.
