The chance is the same in and out of arena. Any rep worthy kill will give you a drop chance.(whether you get rep if in zone, or not if in arena) If you are in arena you will still get put on the rep cool down timer and also drop chance cool down.
The chances are miniscule, exacerbated by the fact teams tend to zone in on a single target. We got a Panacea:Heal drop in practice the other day and that was the first one I'd seen in almost 4-5 weeks...
Questions about the game, either side? /t @Neuronia or @Neuronium, with your queries!
168760: A Death in the Gish. 3 missions, 1-14. Easy to solo.
Infinity Villains
Champion, Pinnacle, Virtue Heroes
So what is the best strategy for PvP IO drops?
I'm planning to start PvP anyway for the fun of it, but I would like to maximize my drop chances, however minuscule they are to start with 
Virtue Speed Junkie
A Simplified Guide to Attack and Defense
Are the chances similar to drops in RV and other PvP zones?
Of course, I'm looking to maximize my chance for PvP drops, so was wondering if I should get active in Arena matches or head out to the zones and take my chances there?
Virtue Speed Junkie
A Simplified Guide to Attack and Defense