I don't have a problem running job of different user on the same compute node.Try this:
1.Create nodegroup TestGroup and add compute node(s) to it
2.In Windows console type : runas /user:user_name@domain cmd
3.Provide password for the user
4.When new console opens with user context type : job submit /nodegroup:TestGroup calc.exe
5.Verify that the job is running in the user context (Owner tab in ClusterManager\Job Management or log in to compute node and check the owner of calc.exe program)
6.Repeat steps 2-5 for different users
As for limitation ,you are limited by resourcces rather than the number of users.HPC cluster is fully domain environment.It would be inconsistent if there is limit for users.As long as domain controller can handle all the user accounts there should be no
problem on HPC cluster side.
Daniel Drypczewski