Yes! They've been using FlightGear to simulate and showcase the craft for a couple of years now. If you're interested, there's a nice collection of demos on YouTube explaining various (unique) features of the vehicle as well as showing the simulator.
Even better news is that you can finally buy a real one for yourself as of this week. If you have the money that is
They've been to FSWeekend the past years, including last year's edition, but I'm afraid you'll need to bring your wallet with you though (even if you work for them;-) ).
One can build pretty much anything in JSBSim as long as there is enough data to build a good model.
Low-level flying — It's all fun and games till someone looses an engine. (Paraphrased from a YouTube video) Improving the Dassault Mirage F1 (Wiki, Forum, GitLab. Work in slow progress) Some YouTube videos