ORS has a fixed concentration of sodium, sugar, bicarbonate and most importantly the osmolality (concentration) etc. Used mainly in diarrhoeal diseases where there are losses of a combination of electrolytes, these help to prevent hyponatremia/ hypokalemia.

See this link for the contents ORS pdf

You could compare the contents of the MRE drink mixes with the standard list and see.

As long as the contents stay in their powdered form and do not congeal together from moisture seeping into the package, the contents should be fine.
Was FEMA giving these out in anticipation of acute diarrhoeal diseases, cholera because of water contamination from the hurricane hit areas ?