Both skills are getting some aggro, but actually every heal is getting more or less aggro. Holy Group Recovery is instant cast and fills up a huge amount of HP. In this case Holy Group Recovery is getting a lot more Aggro than Group Healing Breath. While Group Healing Breath has some cast time the same as Group Healing and does not heal as much HP (Silkroad gold) as Holy Group Recovery.
If you want to see, how these skills work, maybe just get Group Recovery and Group Healing, The more advanced heals are basically the same. Seriously for me it sounds, that you do not have any experience about clerics and you ask about level.80+ skills. Maybe try a cleric in lower level (Silkroad online gold). First, before thinking about high level, if you do not know anything about clericing.
And that about hunting was just an example in Silkroad. If you use Group Recovery, while hunting quite a lot NPC thieves will run to you instantly and stop attacking the traders. Same happens, if you use that skill in any other pt, unless you are STR cleric, but if you are cleric in a pt, you do not really want aggro. So this skill is not even an option for us in pts, as we could not handle several pt monsters running directly to us.