It seems that they are actually built as courier ships usedi n the Federation but not by starfleet. They were later modified to serve as fighters for the Maquis and Starfleet.
http://memory-alpha.org/en/wiki/Peregrine_class
http://memory-alpha.org/en/wiki/Federat ... ck_fighter
This doesn't seem such a crazy idea. We were throwing everything we had into the dominion war. Throwing ships into combat like outdated Mirandas. And I'm pretty sure I saw some Nova's in the mix as well. (Any Oberths?)
Having starfleet round up and arm up civilian craft isn't at all unprecidented. I think most armies in WWII outfitted civilian ships as makeshift escorts.
So besides this couries ship are there any other indications of something we would consider a "fighter" being used by any power? I can only think of the Cell ships from enterprise and the atmospheric craft you sometimes see used.
For example
![Image](http://www.ditl.org/gpaf/GCellShip2.jpg)