If you are shopping for a local level horse my guess would be you are looking for a horse for the 3ft and under?
Alot of the lower level eventers that are going BN and N ( 3ft and under) for amateur and junior riders are already quiet, consistent in rhythm and oftentimes decent jumpers that can take a joke. Obviously this not always the case with every horse at that level but it is often enough that I don't think it would be that hard to find a lower level eventer that can cross over to local level hunters. I would imagine that if the horse is experienced and has a good mind it is worth checking out.
As others mentined it depends on the horse - used to be that a horse that couldn't do the hunters wound up in eventing - I don't think that's the case any longer. Now there is eventing and there's eventing...and who the trainer was.. a good event trainer is going to be just as concerned about form as a hunter/jumper rider over fences - after all going clean does count right?
There be no reason why this particular horse has an event career other than maybe that's their discipline of choice... My horse has done hunters, eventing and jumpers... and managed to do pretty decent - usually in the ribbons. Another horse at barn was purchased to be an upper level eventer but didn't have the speed to cover the ground at that level - that horse is doing great in the hunters at A shows ! Lovely lovely mover.
A friend of mine had an eventer, he was older semi-retired so she decided to take him to a local hunter show series - he rocked it...and came away w/ the year end series award..
So it's not so much the discipline as much as it is the horse's natural talent.
My late mare was an eventer before I got her. She had the looks and talent for the hunter ring, and never looked at any of the jumps. The only issue we had was that she was "hot" and, as an eventer, was used to jumping much more forward and in the bridle than most hunters. She got bored very easily with the slow and steady hunter rounds! But I'd say it all depends on the horse. Good luck!!