They do cover pre-existing conditions however you may need to give some form of doctors clearance that it isn't a current issue, or they cover it and you pay an excess.
Luma. They were incredible with me, I was in ICU for a week, they paid every expense before I left the hospital, no out of pocket, and even checked up on me. It was really nice.
It also didn't feel like they were trying to catch me out, they were actually very helpful when I asked exactly what they needed and even said they'd allow me to lodge the extra paperwork up until 4.30 if I couldn't get back by 4pm.