Honestly, my dog eats hairs all the time, he's never had a problem.
Well except, and sorry to be graphic, but sometimes when he poops, it is left dangling there by a hair he's swallowed.
At which point he comes to me and patiently waits for me to get a paper towel and remove it.
In all the years I've had him, that's the only issue with hair eating that he has.
ETA:I've avoided this thread all day, simply because of what I thought the title said
Although I have had them throw up some pretty nasty things too...fuzzies from blankets they've destuffed, wood chips from sticks chewed on, string from rope toys 'eaten', plastic peices from buckets they've destroyed, etc...but I don't think I have actually experienced an actual 'hairball'...only the kind from the butt...
Come to think of it...I think I would rather take a hairball coughed up from my cats anyday, compared to what I might clean up from what my dogs may have eaten...