Does Projectile Damage passives increase the damage of skills like Fireball?

Title says it all. I was wondering if for example fireball, being a projectile skill, would become any stronger if one were to increase a character's projectile damage. Specifically I wonder if the Iron Grip skill would in any way effect the fireball skill; after all, they only deal fire damage, and not physical damage.

Projectile damage affects fireball.

However, Iron Grip does not affect fireball since Iron Grip increases Physical Projectile Attack damage, so only damage that is all 3 of those is affected by it.

Thank you very much for the reply!