hanging a water hose holder on stucco... do I need to find a stud?
I would recommend just getting a stand. Once you get through stucco it's not sealed and moisture and air gets in and causes rotting behind the stucco.
Most carpenters and cladders may tell you to just spray foam or some sort of sealant will do the trick. But I am a restocking specialist, I have the carpenter and fire flood and mold restoration experience. I tell you to think of it deeply, the stucco acts like cement it stretches and shrinks there for once the sealant is cracked it's not going to expand or shrink with the stucco.
Some will tell you to fill it with stucco. But again unless you are the one who installed it to know the exact brand that was originally used there is different ingredients in different brands meaning again expansion and shrinkage are all off set. I know alot of people won't think it really matters one little hole. But moisture once behind the stucco becomes drops that can infiltrate the tightest spots and go far. Rotting everything behind it. 
But that's just my 2 cents based on almost 2 decades of experience dealing with this stuff.