Saltwater is most toxic to plants because it dehydrates them, causing what looks like burns. Have you had any good snow/rain storms since the storm? (I'm in the Mountain west, we've been super dry this year, but New England is so much wetter I'm hoping your azaleas will have had at least a few good, clean soakings since then.) If your soil has a salt crust on the top, obviously removing as much of that from above root structures before composting would be very helpful.
I did a google search for plants that survived Katrina, found this nice story about a rose bush that survived after almost 2 weeks under salt water in Plaquemines Parish. So maybe two hours under water won't be as detrimental to your rose bush as you fear.
Also, remembering my time in Mississippi post-Katrina, I seem to remember some bulbs coming up on empty lots (the houses had washed away), but their bloom time was delayed. I don't remember irises, but having never been to Mississippi pre-Katrina, I have no idea if there were tons of tubers before the storm.
Good luck! I grew up in Massachusetts, the plant I miss most in Colorado is the azalea. Broke my heart to learn it wouldn't grow here.
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