Redstone wire can travel upwards on hoppers, like slabs and stairs, which is normal and just like on the Java edition. However, a redstone signal can also be sent downwards from a hopper to another block, unlike slabs and stairs and unlike its behavior in the Java edition. Possibly caused by the fix of MCPE-14199 for hoppers.

See this video for a good demonstration/example:
https://youtu.be/rC0zbhGJsLw

EDIT: As of 0.15.90.8, all redstone components can be placed on glass on any side, and glass allows for vertical redstone both up and down, like the hoppers in this issue. I suggest that hoppers be changed to act like upside-down slabs & stairs, and glass, glowstone, sea lanterns, and other transparent, full-cube-shaped blocks act like glass does in 0.16.1. See MCPE-16872.