This thread has been around for so long, I'm going to repeat something I wrote a year or two ago:

You can sing in a loud, rough, "raspy" style and NOT damage your throat, vocal chords, etc. Vocal self-preservation does NOT require that you sing exclusively with a soft and pretty approach. Assuming that you pay attention to breathing, posture, and other such basics, you should be able to find a way to perform in any vocal style without damaging yourself.

There have been plenty of great blues/R&B singers with long careers despite constantly performing in a "rough" vocal style. John Lee Hooker, Howling Wolf, the over-300-nights-a-year wonder B.B. King, and others too numerous to mention. And, as noted above, Gregg Allman.