We are committed to keeping the world of Sanctuary a safe and fair place for all players, and our Game Security team constantly monitors for cheats and unauthorized modifications. All Diablo IV players agree to the Blizzard EULA as a condition of playing the game. The Blizzard EULA explicitly prohibits cheating, bots, hacks, and any other unauthorized software which automates, modifies, or otherwise interferes with the game. This is important to players’ security as well as the game’s long-term...
You can see videos of turbohud used with d3 on youtube. It adds, for example, item/skill texts rather than just an icon, more detailed dps meter, and a larger minimap as an overlay, etc. I don’t know if any of it should be considered cheating.
Also, for what it’s worth, the TH4 site says it disables itself when pvp marked.