I dont know for sure.. but it would not surprise me..
The amont of people that do wheelies on sports bikes now and the amount of damage doing wheelies and touching back down can do to forks and fork seals, I could see how fork seals would not be coverd under warranty.
But again I dont know for sure. I would probably check with a few dealerships in differant county's to see if there was a general consensus.
Also, shouldnt the owners manual describe what is covered under warranty?
and last but not least, check Suzuki's web site, they might have a list of warranty items.
I have never changed seals so I have no idea how hard it is. But if it were me, for $300.00 I would probably figure out how to do it myself.
Good luck..