Damage procs and dot powers
In my experience something like rains etc only proc the damage once. I am unsure of damage auras etc.
I did try to proc off of caltrops and the proc only occured once. Fireball has a burn effect. The initial blast will have the chance to proc the damage but the burn effect or lingering fire damage will not.
The basic answer is yes with a but.
The but comes in because there are a few ways that DoT powers are implemented. The traditional DoT powers (including both Incinerate and Fireball) are normal click powers and as such only have one chance to proc when the power is first used. However location based DoT powers (such as the ever popular Rain of Fire) are implemented as an aura-based pseudo-pet and as such will have a chance to proc every 10 seconds.
Newb question: If I slot a damage proc (ie. Hecatomb %) into a power that does dot damage (ie. incinerate, fireball, etc), does that damage proc only proc once?