I do think they should just remove all the annoying requirement that you need hollow ground to trigger other important parts of other abilities, it's just tedious. Hollow ground should enhance the base ability, not a requirement to trigger other part of the abilities.
Renewal should give armor buff of 300 at base (equal to 50% DR on health) without Hollow ground from the get go. If Oberon stands on hollow ground, the buff goes to 600 armor (roughly 66% DR I think) without the need for allies to step on it because people most likely ain't gonna step on it. Renewal should only drain energy when someone loses health and cost 25% less energy drain when standing on hollow ground.
Your Reckoning suggestion is great. I would add another buff is that, if you step on hollow ground, it will reduce energy cost by 25% as you need multiple cast to strip armor and again with new group of enemy.