It depends on shockie length and shockie shaft travel. Husky twinshocks are a good example of a design that definitely needs spherical bearings, while the Cota 172 trials bike is also considerably narrower at the top mounts, but has no problems using just flex in the bushings.
Whatever you use, do make sure that the mounting pivot axes are perpendicular to the centre lines of the shocks when the shocks are at half travel (to minimise the side loading on the mounts)