The only time the AI uses "bombardment" units is if they capture them. They then fortify them in their cities. When you attack the city, they then shoot at your units before they attack the defensive units. Hey LaRo, Nice plane!
I haven't run across offensive AI cat/can/art. They do actually build them on their own and defend their cities with them, but they tend to not build enough to have a dramatic impact - nor do they build enough to really use them offensively.
I don't think that even if you let them capture your stuff that they will put it to good offensive use. I once had 2 cat's captured and the AI immediately sent them into its own territory despite having a large offensive force on the attack against me.
The good news is that the AI uses planes to great effect in economic bombardment. At least to great ANNOYANCE.
Ai actually uses artillery in the attack(sometimes), but only if he has captured it just ahead, and not has fortified it yet. But he does not protect them, and it is an easy job fore you to recapture it.