Hi. Im a Purser with Emirates and flights out of Australia we do not spray the cabin at all. From Dubai to Australia we do spray the cabin but this is done before customers board. To and from the UK from Dubai we no longer spray the cabin at all.
Emirates does supply supplementary oxygen in either pulse or constant flow at a rate prescribed by a doctor (e.g. 2Lt/min, 4Lt/min, or constant, etc). You need to ask to speak to the medical department in order to get this arranged. The crew are all trained on the supplementary oxygen so there should be no trouble at all. The only problem i have encountered is the mask type so be specific - do you want a face mask or the nasual tubing? Be specific in your request. Most passengers find the nasal tubing best (can't remember the medical name for it), especially for long flights as it doesn't interrupt with them consuming food and drinks.
Hope this helps. If you are still having trouble trying to find help let me know and i can find it out very easily for you.