Aerith touching people does seem to grant some people the ability to see them, but I kind of think it really has more to do with people who have the ability to change destiny simply have the power to see them, especially when they try to alter events like how Avalanche finally sees them when they try to do the Reactos 5 missions without Cloud. I say this because of the Shin-Ra members, only Hojo and Rufus ever see them, yet Hojo tried to change history by revealing Cloud's true nature to him, whereas Rufus just seems to be able to see them whereas Tseng couldn't.

The only people who seem to know what the Whispers actually are seem to be Aerith and Sephiroth, though Red XIII knows a little after Aerith touched him and imbued him with knowledge. These little moments are probably why a large part of the fanbase is theorizing that Aerith and Sephy are somehow channeling their future incarnations from the Lifestream.