The rules engine is composed of three main roles. This gives various organizations the ability to segment duties amongst the various contracts for increased security.
From a security standpoint, it is not advisable to use one account for all roles in a production environment, but there are no technical limitations prohibiting the use of one account for all roles.

Calling Contract Admin

Manages which policies are checked when a contract interacts with the rules engine.

Policy Admin

Controls what is checked during Rules Engine evaluation for a given policy and configures all policy settings.

Foreign Call Admin

Controls who is eligible to invoke permissioned Foreign Calls and configures which Policy Admins may leverage them.