I guess Ron's answer was a bit too cryptic. The basic "general" answer is - No, it is not true that orchids need to be kept away from other houseplants. If you look in any public conservatory you will see different types of orchids grown together with all sorts of other "tropical" plants. In the wild terrestrial orchids often grow in close proximity to other plants while arboreal orchids actually grow w on other plants. If you are talking about combining two different species of plant in a single pot then there may be some plants that would cause problems for a particular orchid species; if so I don't know what they are. In general you just need to ensure that the plants you are growing near each other like the same light and humidity levels, and if you are growing them in the same pot that they like the same type of soil or growing medium and amount of watering. You also need to make sure that one plant is not so vigorous that it takes over the whole pot.
