Actually, I do think the original poster might be onto something here... but he posted the wrong design.
This is the 2nd generation Winged Defender. When performance enhancements were implemented and a relocation of the warp nacells to the former weapons mounts and vice-versa.
It doesn't look that much like the Jem Hedar ship.
But I believe that's because that's because the poster wasn't looking at that Winged Defender when he saw the resemblance (and the resemblance is mostly only from the front profile view, not the top).
But compare the front profile view of the Dominion ship with the original Winged Defender (as seen in FASA's Star Trek III version of the game).
You see much much greater simularity. Note the trapezoidal front even. Some aspects seem a bit reversed/flip, but there are a striking number of similarities. Pretty much, just flip the old Winged Defender upside down and you have almost the exact profile of the Dominion ship. In fact, the trapezoidal "cockpit" of the Winged Defender is simply pushed down. But it's even maintained in the Dominion ship.
Furthermore, you could even see how an artist may have started with this and expanded it from the top view. Take the cockpit of the WD, and split it to make it look different. And what you almost see is the Winged Defender morphed with the Nova battleship. Take the old Winged Defender's front view, and the Nova's top view...and you pretty much have the Jem Hedar ship.
Oh my, to quote Takei... I just looked at the side view of the Nova. Notice that if you remove that big monstrosity on the tale. The side view is near identical to the Nova's.
So yes, I am going to have to give it to Knight Templar. The Dominion's Jem Hedar warship is essentially an amalgamation of the Romulan Wing Defender (v.1) and the Romulan Nova battleship.