Affected Platforms:
Windows 10: Yes
Xbox One: Yes
iOS: Yes

Mobs of all types are able to spawn on redstone components. Redstone being spawn proof was specifically added to java around 1.9, A lot of people use redstone dust to mob proof builds. it's a simple way of preventing accidents while not torch/slab spamming everything.

Please note that mobs will spawn on top of ALL redstone components.

Dust
Repeaters
Comparators
RS Torches
RS Lamps
Observers
Droppers
Hoppers
Dispensers
Rails
Pistons of both types.