sounds like running towards the dictator trap with open arms. If I wanted to get to Mars then I would suggest its poor company behaviour to suppress criticism like this as I doubt that doing so to protect personal twitter behaviour is helpful to the org's mission statement.
Arguably it depends somewhat of the skill of those hired but if that's arbitrary (i.e. their skill isn't related to the firing) one can easily argue that SpaceX's management practices are extremely questionable right now. So from an 3rd party employee's perspective today you have to tell the boss he's fucking shit up if you _really_ want to get to Mars.
SpaceX are quite literally the only company on the planet capable of what they're doing. Elon is the sole reason Mars is even a possibility, as the rest of the world had given up on it. Same goes for EV's.
So yes, for all intent purposes he is their employer.
[1] https://www.quora.com/What-percentage-of-SpaceX-does-Elon-Mu...