The blanket answer is: "Yes". I've heard stories of relays bouncing all over the country, from originating stations in Katrina's Ground Zero, in an attempt to get word out. Here's one from NPR ("All Things Considered", August 30, 2005)

More to the point: KD5QEL's blog is probably representative:

PLEASE DO NOT attempt to pack yourself off to these areas, by yourself, without coordination! The needs are great, but going into these areas all willly-nilly will only cause additional problems for the folks who are already there trying to handle the situation. They need TRAINED operators, not just people who happen to have an HT.

And please be aware that the conditions in these areas are still deplorable. It has been recommended that volunteers have booster shots for diptheria and tetanus, as well as an IMG, which is a shot for immediate protection, good for three months, for Hepatitis A. (If not the IMG, having had the regular immunization series for Hepatitis A&B would suffice.)

These deployments will be coordinated through the ARRL. If you, or a team of you from any of our ARES groups is already on stand-by and available for deployment, please send [the information form] to our ARES leadership for relay to the ARRL."

[ ... snipped...]

You will be staffing 250 Red Cross shelters and 30 kitchens for an indefinite period of time.

You will be living in hardship conditions.

More information at Ham Radio Online, and WX4NHC at the National Hurricane Center.