I think this would work if you were all growing similar types of orchids with similar needs, but it would have to be with rules - if you have allotment gardens in the states, then you will be only too aware that one person's approach to tidiness is totally different to another's.
Ive been to a few businesses that have other peoples collection growing in them. It wouldnt hurt to inquire about it with a commercial grower or someone that has a larger greenhouse.
Well when you put your plants in an orchid show, they may be right next to someone else's, and pests can certainly spread, although it's for a very short time.