I'd put Rainbow Dash in the category of seeing Ammy completely, if only because things like Unicorns, Pegasi, and other such mythical creatures are just so common in that fandom that it'd be odd for her not to be aware, methinks. The choice is ultimately up to you though, I'm just giving my own thoughts.

Ven and Riku are a liiiittle bit harder, since I'm not as familiar with their canons. I want to say Ven would see her quite a bit, but not completely, because if he's not a strong connection to light (which is basically what Amaterasu is, more or less) he'd notice her to a certain degree. Iii...honestly dunno about Riku. I'd like to discuss more, but I think he'd see her somewhat as well.