My farrier successfully trims my horse's hi lo and has actually managed to reduce the under-running of the low heel, all with shoes on.
The most important thing I've found with treating hi lo, beyond radiographs and a good farrier, is frequent trimmings. My horse is trimmed and reset every 4-5 weeks. My farrier jokes how he would love to be out there every week to keep the horse balanced haha. Another important thing to consider with a hi lo horse is the alignment of the joints above the hoof. The left and right knee should be at the same height!! Working a horse with such an imbalance can cause a plethora of issues.
They say money doesn't buy happiness -- well happiness doesn't buy horses!