These are not pyschosomatic illnesses. I think this hypothetical condition qualifies as a disability. There is a major life function that is affected and is substantially limited. There are reasonable things that can be done. There are some things that are unreasonable.
Reasonable accommodation applies to every workplace.
You might consider asking your staff to refrain from using scents and establishing a fragrance-free workplace or zone. Another step that could be taken is to provide the person with the sensitivity with an air filter or move their workspace to an area that has lower traffic. Perhaps there is some way that they can participate via a web conference or chat room from another part of the office or building. These are low-cost, minor adjustments that should not have a significant impact on the company budget. The employee is still part of the workforce and has received adjustments so that they can continue to interact with the rest of the office.