I'm going to use the rhetorical device of picking a single of your statements:
If the Bismark, loose 'somewhere in the Atlantic', was a credible threat to merchant shipping, then so is this.
Let's use the Bismarck as an analogue to our airship carriers. The differences would be that the Bismarck was far more armoured (and able to survive much more), while also being far harder to detect (due to it being on the sea while the airship would be in the sky, with no horizon). Speedwise, I'm not sure. The Bismarck had 60km/h speed, while our airship is fast enough that our biplane fighters (max speed 230km/h) could dock. So it's probably something between 60 and 80 km/h for the airship. Not really a decisive factor.
Now, the Bismarck was killed due to attacks by carrier-based torpedo bombers from about 120km distance.
I am assuming for now that we only need a single fighter to come very close to the airship to be able to down it. This may not be accurate, but probably will be shortly after we first use them. Hell, a pair of small bombs with contact detonation should rip the airship apart (if they detonate on fabric contact, which is not certain).
Now, for a raiding mission, we can probably expect not more than two or three airships (cover more area, and we won't devote that many resources to them). So let's say about twenty aircraft deployable.
The Morovian's twin-engined bombers range is unknown, but I would assume it to be about 300-400km combat-range (get there, fight, get back). With searching (though that can be done by other means) this means a let's say 250km corridor around their homeland where we can be pretty sure they can kill our airships by sending twenty, thirty fighters of their own there. And even if they don't manage to kill it the first time, they can refuel and resupply and come again, while the carrier's planes can't be replaced until returning.
So, to sum up, I'm pretty confident that using an airship carrier for raiding will most definitely end with said carrier destroyed with too few gains.
And I believe that while there are direct routes to trade, every merchant captain will gladly do a detour around a war zone with commercial targeting. See, for example, the routes adopted during WWII.
And, lastly, said air power could probably be reduced pretty well by installing anti-aircraft weaponry on the merchant ships. Fairly cheap, and even if they don't prevent the ship's sinking, they attrition the planes away.