This does not cause any problems at all. You can specify the maximum number of virtual users that an Agent can simulate either from the Agent menu under the SETTINGS or via the console by selecting the Agents tab at the bottom of the console to view all the Agents connected to the console and then right clicking and selecting SETTINGS.
Now the number of virtual users that a workstation can simulate before it gets bottlenecked, usually by CPU but can also be memory or network, is dependent on the workload that you are running. Such things as how long it takes for the transaction to execute, the amount of latency, result set size, can affect the number of users. So it is a best practice to run the test first to see how the workload affects the Agent so as to set the optimal maximum number of virtual users per Agent so you can get the most out of your heterogeneous testbed.