I don't think there's much added value to using Selenium on top of Jmeter, or any java based load testing tool.
The idea of load test is to simulate the traffic profile of as many users as possible to test if a server can handle the load. Selenium is designed more for user acceptance testing, where you are testing on the user experience.
You can however, use a load testing tool like Jmeter to take the load to say 90+% capacity, then run a separate Selenium test to verify if the user experience is greatly impacted. This can give you some insight on how well your services degrade.
Running multiple instances of Selenium will not buy much on the load testing end (in fact take away since you're wasting resources), and also multiple instances of selenium running on the same machine will introduce a large amount of unreliability in the test itself, and not produce any useful results.