How can we incentivize volunteer rescue forces like the Cajuan Navy which assisted in Louisiana? State-sanctioned militias in the state of Louisiana were an important part of the state's natural disaster response. Tiny boats went off into flooded areas to rescue people. These rescuers may have broken some laws but were allowed to do it because of the broader humanitarian interest they served. 

Question: How to incentivize people to get a permit?
The incentives to get a license to become a member of a Cajun navy would be in times of peril---such as hurricanes--- to get to the disaster area quicker. But, this is not a great one. What could the state do to register people in times of non-crises? Tax-breaks? I am not sure
The United States Code provides for such a force and I believe Louisiana has one.  They are usually called "state defense forces."  They are a parallel state force with the state components of the National Guard.  They are not subject to call up by the President and serve in policing and emergency management roles in the states.  Not all states have them.  In some states they are both voluntary and require you to provide your own equipment, in others, they are fully funded.

I believe the Military Department of Louisiana has or had such a structure.  Nothing prevents the State of Louisiana from providing either pay or tax incentives to organize and manage the membership and to permit it to exist broadly.  Considering the frequency of natural disasters in Louisiana adding formal training and incentives to such a force would benefit all parties involved.

Imagine the effectiveness of the Cajun Navy if it had received formal training and worked within a planned response.  In most states, these are token forces primarily made up of ex-military who wish to continue service, but no longer wish to be in a potential combatant role.  They serve a small, but often important role, in mitigating the immediate effect of a disaster, but I don't think the states actually think of organizing any large number of people.  Most likely this is because they exist, but are so small that legislators forget they exist and don't expect much from them.