In the end, although I was prepared to fight the cost, I didn't end up having to pay anyway.
I called Hyundai USA thinking that perhaps Genesis owners would get better treatment and I'd find an understanding agent ready to pressure the dealership or reimburse me for the stupid cost. No dice. He explained that since the recharge was out of warranty the cost was on me even though the recharge was only necessitated by a warrantied leak.
When I had first arrived at the dealership I explained to the service tech that based on my understanding of the problem, looking at schematics and other experiences, I suspected the compressor pump had seized. (See this description of a compressor failure on this site, which matched my experience quite well:
http://www.genesisowners.com/hyundai-genesis-forum/showthread.php?t=2533&highlight=compressor ) He more or less dismissed me with a cursory "we'll look at it". He then came back with the leak story and the $150 refrigerant recharge cost.
After recharging the problem persisted. They put one of their "platinum" techs on the problem and about an hour later, sure enough: the compressor pump had seized. It does feel nice to be right.
Since the recharge was unrelated to the problem anyway, they did not charge me for that of course. Too bad; I was prepared for a fight.
In fairness to them, apparently this was the first case of a compressor pump seizing in a Genesis in Minnesota or anywhere nearby so they had reason not to suspect it. Still, I hope no one else gets told they'll have to pay part of the costs of a warrantied repair.
My compressor should be replaced by Friday, when they get it in.