People plant everything else in group planters so why not orchids?
The nice thing about having multiple orchids together is that it prevents root-rot as more roots dry the medium out faster. When they bloom together, the display is nicer. I have two cattleya siblings together in a pot and I am getting some new Pleione orchids and planning to put them all in one bulb-bowl when I pot them up for next spring. I see nothing wrong with potting up orchids together to make a nicer display.