Do ISV's who have solutions outside of the Microsoft Dynamics GP solution need a Limited User?
In most cases no. A license is no longer required if an ISV or partner created customization hits the SQL database directly even if they use eConnect or Web Services. If the ISV extends the GP solution and provides more functionality and better user experience an additional license is not needed. The exception to this rule is when it's a multiplexing scenario. If an ISV copies or replaces large portions of the application to reduce the number of devices or individuals that access or use the Microsoft Dynamics ERP solution by pooling connections which would be multiplexing, does not reduce the number of Full User licenses required. When connecting to Microsoft Dynamics through a pooling resource, users must be licensed with Full User or Limited User licenses in compliance with the software license terms and the pooling resource must limit the number of simultaneous users to match the number concurrent users licenses acquired specifically for the pooling resource.
A good way to think of it comes down to common sense. If the ISV product adds functionality, improves the user experience and gives customers more value then its not multiplexing. If the ISV is providing functionality that does the exact same thing in the exact same way to reduce the number of users, that is multiplexing.
Keep in mind a SQL licensing still applies.