Yes; satellite boards tend to have conformal coatings, it helps but it's not a complete solution. (The coatings also help avoid shorts from junk floating around, and launch vibration.) Because of the inherent unreliability and difficulty in replacement, they also try really hard to avoid lead-free solder requirements.

Yes? In my experience (some spacecraft electronics stuff) this is also on the list of things where we think conformal coating/potting helps prevent tin whiskers. But there are still instances where Tin whiskers have grown and pushed through conformal coating on a PCB.

Edit: Go look at the more detailed response from robomartin

No. Can't prevent it. Yes, they can push through epoxy or buckle under it (which isn't a solution). Read my longer answer for details. These things are a nightmare.