Is this true?
 

I have some orchids sharing a basket, Neof. and Encycl., and I found this on orchideria.com "Some plants produce a chemical reaction in their fragrance that is a clear sign that nothing should even try to live near it. This aromatic battle is called allelopathy. This is also why not all orchids make the perfect pair when mounting together. Some might send out signals that they prefer to be alone."

Is this real and are there resources to find which orchids do well living on the same mount?

I haven't heard of orchids doing this.

After a quick Google search using alleopathy orchids I found a study via researchgate.net
I read the summary of a study of preliminary research into this written in 2014.
I did download the full study but it was written in Cyrillic.
From the summary it seems this result was seen in the protocorms and seedlings with in one case mentioned had "massive blackening and death during joint cultivation"
Also mentioned a few pairs that worked well together and others that did not.

Generally speaking, it is better to grow individual plants separately, if for no reason than to reduce the chance of pathogen sharing.

I thought "scent" was meant to attract pollinators, not to scare something away.

Orchids (likely all plants) contain phenolic glycosides. When tissue is damaged, bacteria can oxidize them into active chemicals that may smell or taste bad to the attacker, thereby providing some defense from further attack.

There has been some thought that such chemicals can fend off the root systems of plants growing too closely, and that may be why activated charcoal is added to the agar-based media in flasks.

Interesting points, especially regarding the charcoal.
I have occasionally wondered if having charcoal in the pot would reduce the amount of fertilizer the plants get.

Unlike the stuff used in flasking, the charcoal used in potting media isn’t “activated” charcoal, so it’s absorption is similar to some bark products.

Thanks that clears that thought up!

If you find only one study on this, it may or may not be true of orchids. There are a few plants that are known to use chemicals to eliminate the competition...black walnut trees are famous for it, for example, but it is not a very common ploy. Plants tend to eliminate competition by either growing quickly and having a dense canopy or just crowding out other plants with offsets, speedy, effusive propagation, roots or leaves.

One orchid crowding out the other would be a good reason to give orchids space when mounting or potting them.

Yeah, the whole article sounded... mmm... fake and dumb to me. I have a B. Sci. in biology but I'm no botanist so when it comes to plants I can be fooled. To me allelopathy is when two genetic characteristics (the alleles) combine to produce a fatal or harmful developmental disorder. My concentration was marine biology but I never studied phycology in depth. Oh and when I'm not in a classroom or a lab I will oversimplify because most people I know aren't biologists, although maybe here on orchidboard I should go ahead and split sugar production from carbon fixation instead of lumping processes not involving photons under photosynthesis but usually I just lose people if I get that detailed, and I'm not a botanist either so I'm a bit rusty (to put it mildly) on plant respiration and metabolism. Maybe I'm just too long-winded as well, I'm sure I've lost most of you by now ;)

I'm with you, it seems dubious. I would need a real study to believe it.

That said, allelopathy is very much a real thing. It is usually a plant somehow altering the soil around it so other plants can't grow. In the case of the western US we have a problem with invasive salt cedars filling their leaves with salt and dropping them, effectively salting the earth around themselves. The result is huge areas of river basin where nothing but salt cedars grow. In this case it's very destructive but still, Its really interesting to learn how that stuff works.

I am doubtful that fragrance or other gaseous chemicals can have such a dramatic effect in the environment around a plant, but I have learned many stranger things studying plants so I'm totally open to being proven wrong...

I'm not sure why people make stuff up about orchids, they are stranger than fiction!

Getting back to the root of your concern, I really think your basket with two species will be completely fine. Please post a photo sometime!