Can third party invoice and payment be interfaced to AR?

We have several third party billing systems in use and several new systems coming on line within the next few months.  Several of these third party systems basically deal with a  "cash and carry" type of transaction.  For example, our planning department is going with the Posse Land Management System Software for building, planning, engineering, code enforcement, and other land management activities.  Posse will handle the customers' permitting needs.  Through the Posse work flow process, the permit is granted and created for the customer.  Once the customer pays the associated fees, they are given the permit.  This is a one