ObjectGen is a tool for generating test objectives from use cases. ValueGen is a tool for generating operational variables and combination of values from use cases. Although ValueGen needs the artefacts generated by ObjectGen, both tools are independent.
C. Mingsong, Q. Xiaokang, and L. Xuandong. AST '06: Proceedings of the 2006 international workshop on Automation of software test, page 2--8. New York, NY, USA, ACM, (2006)