The list of user types is defined twice (once here and once in CustomOrganizationUserForm). Could this not be defined in a single place (preferably with the descriptive text passed through i18n).

Given that this user types stuff is, in effect, a facade to the model, perhaps custom_organizations should have a models.py file which defines user types, plus any other supporting functionality. That would mean that the details of how this facade work can be kept out of the forms and views.