Test "300 threads" from VPS scripting, is it possible? how?

A certain captcha solving service offers "300 threads with unlimited solves" plan. We want to test the service. Is it possible to properly manage the 300 threads, provided we have VPS to run scripts from? Possible languages/environments to use are Node.js or JAVA or PHP or Python.

If yes, explain how?

My partner has critical mind of that:

All threads will be divided by the number of processor cores, and those that are located on the same core will not go parallel, but will simply transfer control to each other. Kind of ineffective...