It's all a matter of personal taste, and common sense. Some mods can be considered cheat mods (e.g. "In my mod, I just added a sword of Mass Destruction which causes 20000 fire damage in a radius of 300, you can find it in a barrel at the Census and Excise office in Seyda Neen"), while others, while they still add weapons, armor, NPCs, quests and so on, can't be considered cheating.
A mod that would increase the variety of "common" weapons, by adding flamberges, flails, gladiums, and anything else that fits in the gameworld (i.e. no bazookas, no pistols, but no rapiers as well, because I'd think that a rapier would feel out of place in Morrowind) wouldn't be "cheating", because it'd give no advantages to the PC.
A mod that increased the range of spears, would give the player an advantage, but it wouldn't still be "cheating" in my opinion, because it's more like a fix from an error made by Bethesda. Why should spears be as long as, and even have the same range as a claymore?
Speaking of which... does anyone know of a good mod by which I can increase (even graphically) the length of spears, and maybe get pikes too?