Offline "trainers", etc. are technically hacks and generally not forbidden and some stuff like real time stat monitoring for MMO games are a bit of a grey area.
Hmm, can't imagine any hacks (by any definition, whether it's a .dll injection, memory reading or writing, etc) would be deemed as acceptable in any companies terms of service agreement, especially for a multiplayer game. Most of them even include macro usage these days as a terms of service violation.