Black Waltz said:
Wrong, wrong, wrong. Corporations at this point will simply make the AI's maintainence untennable, forcing him to lower science etc and crippling economy. It's fairly cheap to spam your corp to them as it will pretty much enable you to win unapposed - especially if the human builds his Corperate HQ in his Wall Street city.
There is a certain element of trade off. One, corporations can provide a worthwhile amount of resources for their maintenance costs, though this is substantially more difficult when the corporation is foreign. I would still be wary of dropping Sushi or Mining inc into high food or production cities of the AI.
The second point is that once an AI has a corporation present, even if they didn't found it, they begin to quite justifiably horde the resources for it. This in turn makes it impossible for you to trade for them, thus weakening your domestic corporation branches.
The simplest way round this is to found separate corporations for domestic and foreign use. Keep the good ones like Sid's Sushi for yourself, and spam the weaker ones to them. If they already have aluminium and oil, Standard ethanol and Aluminium inc don't do very much for them. Civ jewellers is another weak one unless they're going for cultural victory.
As to whether it's cheating - I'm dubious on this one. It certainly weakens them, but if they stick to free market (yes, you can make it hard for them to keep that) and courthouses it's far from impractical. Also, the AI does use the same tactics. I'm seen the Ai spam cretive constructions to all my cities, which was irritating, but not crippling. Granted it was too late in the space race for it to be much of an issue. I'm reluctant to class a tactic which the AI uses as "cheating", particularly when it's virtually the only part of corporations they use effectively.
Hopefully the (proper) patch will beef up the AI's use of corporations, which is downright nonsensical much of the time, and maybe tone down their use as a weapon, making the trade off of spamming them more serious.