in my opinion it depends....if as spoken your following a guide word for word in a puzzle game that says 'go here/do that' etc..yes its cheating, by something by Starcraft...dark souls....doom or so....where you wish to 100% it but cant find those last few secrets or as in your case OP, doing Starcraft on brutal (I feel for you....its hard..haha : P) I personally wouldnt consider getting hints or pointers cheating.
Now on the flipside if your using guides to find exploits/find some way to hinder the enemys movement and cripple them through a glitch etc, then yes, that I would consider cheating, (to a scale).
By that I mean for instance in your case, SC2, lets say theres a little base in a far side corner that pops out more mobs then usual...no it wouldnt be cheating to know its there, seeing as its still up to you to find a way to nuke it/cripple the enemy in that respect. On the flipside lets say the enemy force can only use ground mobs and your Terran and the guide tells you to hover with your main base/spawn a crap load of flyers...that..would be cheating then imo. Not cheating as a rule of thumb but...cheating as in, you didnt find that out yourself.
Edit: Edited for clarification.