I dont know exact difference between these two tools. But sharing informaion about Vistex.
Vistex is the global leader in pricing, contract, and incentive management solutions and services. Some clients choose Vistex to manage master data, contracts, pricing, rebates and incentives.
Vistex, is a third party software company which provides its solutions for SAP powered by the SAP HANA platform. Vistex is an embedded solution within SAP that uses the same master data and handles complex customer, product and vendor data maintenance requirements
Regards,
Kulbhushan