The AI cannot cheat in this game. It has the same metal income like you, the same vision like you, etc.
If you still don't believe me, when you play a game in the online lobby (you can make a custom room with just you and AI opponents), you can go to your user page (click on your name on this forum) afterwards and there are replays of those battles (without the fog of war). So you can see how the opponent played.
Edit: to add - most new players (including me, when I started) underestimate the importance of expansion. Unless you control 50 % of the map, or there is a huge no man's land in between you and your opponent, the opponent produces much more metal than you and just outbuilds you. Zero-K is a very aggresive game, you need units and units and units and unless the map is small, static defenses are a bad idea. You can see it very well when looking at some replay (or look at replays of some very good players).
