>>22409214It's breedable if you have a Heavy Ball female, but not every Pokemon is legitimately available with it. Hidden Abilities didn't exist in Gen IV (including HG/SS)
Hidden Abilities + Apricorn Balltism = Illegal/Hacked
And in this case, Aron was only available in HG/SS in the Safari Zone, so you couldn't catch it with a Heavy Ball.
Ctrl + F 'Aron' here to see all of its legal ball combinations.
http://www.serebii.net/games/geniiiball.shtml 