The dogs I've seen with broken teeth after antlers have pretty manky looking teeth. No-one can answer if its underlying bad teeth (usually the reason for giving them antlers) or the antlers themselves causing the problems.
I feed them but its a risk you weigh up
I would give a pup the split ones and monitor.
My lot are raw fed, and when the youngest was teething she enjoyed a lot of frozen wings - chicken or duck and single beef ribs. It depends again on the dog - my middle dog is a gannet so even as a pup would have tried to swallow them when they got small but the other 2 wouldn't. RAW bones have a very low risk of problems. Its cooked bones that splinter and cause problems
Anco roots are supposed to be good but I've never used them myself.
Have you tried stuffing the kongs? You can use all sorts (and freeze them) - mine love blended banana and yoghurt - poured in and frozen keeps them quiet for hours, or soft food
Will have a think what else we have kicking round the house. I've had 2 chewers
Whatever you use there is a risk