Hey Jen! Thanks for posting - I'm the community manager at Level 99, and replied to your tweet through our account.
The answer is that hero abilities absolutely affect leaders if they say "your unit" - your Leader is a part of your Unit, which is the entirety of your side of the map.
If an ability says "your heroes" then it doesn't include your Leader.
I hope this helps!
Hi JR-- can you speak to the issue of Berserker vs Lixis specifically?
Berserker's vanguard ability does not mention the unit. It says: Takes 1 less damage from attacks, and has +2 attack strength.
Lixis's ability is: "all opposing heroes take 1 damage at the end of each wave."
The question then is whether Lixis's ability is an attack? I would argue it is not an attack, and that therefore the Berserker ability would be inapplicable.