On the other hand, the design looks extremely generic - this model and its big sister are encountered all across the galaxy. If it's a good and easily available design, why wouldn't Starfleet make use of it? Everybody is an enemy of Starfleet at some point or another, but an ally later on; giving money or other compensation to the people who provide ships like this need not be contrary to UFP interests.
Although we could always postulate that all Starfleet ships of this design are actually war loot. Qualor II had its share of alien vessels, including a veritable clan of ships previously seen operated by Talarians. A past war with that culture is already established; perhaps captured transports saw lots of use even if captured destroyers were deemed useless?