The inhabitants of the planet were Maquis, not Federation. They also  evacuated in time before the trilithium resin affected them.
		
		
	 
Both of these claims are dubious.
"For the Uniform" is the first time anybody refers to the concept of  "Maquis planets". Until then, the Maquis had been a paramilitary  organization operating on several locations, including planets in the  Demilitarized Zone, planets in regular UFP space, planets in neutral space, locations in Bajoran space, and apparently (VOY, esp. "Non  Sequitur") even Earth. By that definition, Sisko would have been  justified in bombarding Earth!
But let's assume for assumption's sake that every child and cripple and  pet rodent on that planet was a fiery-hearted Maquis terrorist. Sisko  meets Eddington in space and says he is going to bombard the planet with  a few kilograms of a highly poisonous chemical. Eddington does not  believe him, and the odds that he would have relayed Sisko's threat down  to the planet are slim; Sisko himself certainly did not contact the  planet, and only traded threats with Eddington. Sisko then fires the poison torps anyway. And  sure enough, within minutes or less, people down below begin evacuating.  Why? Surely not because they had advance warning (because they had  none). Surely not because some atmospheric researcher somewhere on the  planet (do fiery-hearted Maquis terrorists have those?) saw a needle  twitch on her instrument for detecting extremely rare poisons (because  who listens to people in lab coats, much less understands what they are  talking about?). Surely not because dense clouds of evil-looking  substance blocked the sun (because the torpedoes only carried a handful  of the substance, not enough to create visible clouds). Virtually the  only possible explanation for these hardy settlers and merciless  combatants to uproot themselves in a matter of minutes is if people  around them began to die in horrible convulsions. Not cough and turn  slightly greenish, but die, and die horribly. Otherwise, these people  would just stiffen their upper lips with a hypospray, batten down the  hatches, and wait for their ringleaders to inform them how to best fight  back.
When a planetwide evacuation is inspired by people dropping dead, it's  guaranteed to fail. If these Maquis terrorist grannies and murderer  babies all carried TAS style life support belts or Israeli style gas  masks every day, every hour of their normal lives, then it's possible  that relatively many of them would make it to the evacuation ships  (which a Maquis terrorist fugitive planet might indeed have for 100% of the  population, even if no other semi-stable colony would conceivably have  the reason to prepare that way). If no portable personal life support was  available, the evacuation would become less and less efficient by the  minute, and mortality would surely approach 90% at the very least.
	
	
		
		
			As explained in almost every episode since the Maquis were developed,  they used to be Federation citizens, but they all gave up their status  as Federation citizens when they refused to leave the DMZ.
		
		
	 
Umm, nope.
In TNG "Journey's End", a single planet in would-be Cardassian space  (not the DMZ, which wasn't even on any drawing boards yet, but  Cardassian space) decided to abandon UFP membership in favor of  Cardassian Union membership; every citizen there became a Cardassian  citizen. In the later and more or less simultaneous TNG "Preemptive  Strike" and DS9 "The Maquis", a DMZ had been formed, and consisted of  UFP planets and Cardassian planets, all of them respecting their native  law but in addition agreeing not to host any sort of a military force.  There was no mention of neutral planets or third-party planets there  whatsoever.
In "For the Cause", when Eddington defected for good, he said the Maquis had left the UFP.
	
	
		
		
			"Starships chase us  through the Badlands  and our supporters are harassed and ridiculed. Why? Because we've left  the Federation, and that's the one thing you can't accept."
		
		
	 
However, in "Blaze of Glory", Eddington (observing the carnage of the  last remaining Maquis) lamented that the Maquis were only considering  declaring themselves (that is, entire planets of theirs) independent  from the UFP when the Dominion came and wiped them out.
	
	
		
		
			"We were winning. The Cardassian Empire was falling into chaos. The Maquis colonies were going to declare  themselves an independent nation."
		
		
	 
Apparently, then, Eddington in "For the Cause" is only saying that the  Maquis criminals have left the Federation, not that their "supporters"  (the expression he uses, apparently referring to the colonists whose  hospitality they exploited) would have left.
That means that everybody on the Maquis planets, including the criminals  and their noncriminal supporters, was subject to UFP law and  respectively deserving of UFP protection. Staying in the DMZ would not  remove UFP protection nor the obligation to observe UFP law to the hilt.  Becoming a Maquis terrorist would. (That is, a criminal would of course  not obey the law - but he would still have rights within the UFP legal  system).
Timo Saloniemi