Well, I'm gonna say what I said on chat: any single player flash game is playable offline, and its more like a feature of flash games rather than an exploit. I always have elements loaded when I'm on a trip somewhere and I dont have a permanent connection (or if I have weak connection).
Grinding offline wouldnt ever be considered a "problem" if you're not T50. I dont think anyone would ever see it as a problem if your first deck wasnt a farm, but rather if you just switched "normal" decks.
So, IMO, the only issue here is the farm decks in general. If its okay to have farm decks up, I dont see anything questionable with playing AI offline. If its not, then its not okay to have farm decks in general, and the issue has nothing to do with playing offline.
Anyway, you may found this out by "accident", but I assure you, Zanz knows about possibility of playing the flash game offline. IMO, if he didnt think its okay to do so, he would have wrote this in the rules section, just like he knows that its possible to program bots to play for you, and he DID explicitly forbid it in the rules. Its the perk of any flash game.