The ships on the cover of Fleet Action are Hakaga class carriers that are mentioned in the book. Of course, they don't look exactly like a typical Kilrathi ship, but who cares? That's the Tarawa on the cover of End Run. Tarawa is an escort carrier (also referred to as "jeep carriers" , if I'm not mistaken, and "Wake Class" carriers).
For Action Stations, we haven't seen any of the ships form that period. For all we know, one of those could be the first TCS Concordia. Or perhaps the mothership of the race that dropped you off here. The helmet looks like some sort of poorly done Halloween costume, and the girls . . well . . . I'm assuming they're just on the cover to attract the interest of people who judge books by the cover.
The only cover I'm not entirely sure about is Freedom Flight, because I know that isn't the Bonny Heather, and it doesn't look like any other class of ship/fighter mentioned in the games or in the book. I'm assuming it must be the Kilrathi installation that they infiltrate.