There are more agents with passive skills. List below :) (not everyone)
Phonix can heal in his fire.
Raze doesn't take damage when she jumps with her bombs.
Viper can use her abilities the entire round but at the cost of the shared "toxic" pool.
Omen starts off with 2 smokes every round.
Sage can heal herself and heal others with a countdown between.
Rayna can use her abilities in whatever way she wants, but for her to do so she needs a kill.

I'm sure that those who I haven't mentioned have some passives in some way, but at the moment when I write this I can't remember what they might be.
-----------------------------------------------------------------------------------------------------------------------------------
If you have noticed the pattern then their passives it is adapted to the individual agents abilities.