Some elements of the cholinergic crisis can be reversed with antimuscarinic drugs like atropine or diphenhydramine, but the most dangerous effect - respiratory depression, cannot. 
The neuromuscular junction, where the brain communicates with muscles (like the diaphragm, the main breathing muscle), works by acetylcholine activating nicotinic acetylcholine receptors and leading to muscle contraction. Atropine only blocks muscarinic acetylcholine receptors (a different receptor class than the nicotinic receptors at the neuromuscular junction), so atropine will not improve the muscle strength and ability to breathe in someone with cholinergic crisis. Such a patient will require neuromuscular blocking drugs and mechanical ventilation until the crisis resolves on its own.