If the Omegas will be rolling off a 24 dB per octave at 100 Hz, that's plenty steep and the only question is "which sounds best". So once you have the Swarm hooked up, try it both ways. In some cases the midrange will sound more open and less boxy with a port than without.
Unported, the Omegas may inherently roll off at about 12 dB per octave starting fairly high up. That can work against you, as their net rolloff would then be 12 + 24 = 36 dB per octave, possibly resulting in a narrow dip in the crossover region. Then again, there is a possibility that asymmetrical rolloffs would sound better under certain circumstances.
With the port in place, the inherent rolloff probably doesn't start until we get about an octave below the crossover frequency, and that's far enough away that I don't think it would raise any issues.
So my short answer is to try it both ways, but my guess is that both the transition between Omegas and Swarm, as well as the midrange from the Omegas, will be a little bit better with the ports unplugged.
You can also experiment with reversing the polarity of one or two of the Swarm modules. For a while I used an X-polarity configuration, with the left-front and right-rear module in normal polarity and the other two in reverse polarity. This sounded very spacious, but ultimately traded off bottom-octave impact. So now sometimes I reverse the polarity on just one sub, and sometimes not on any of them; depends on whether it's a small room (with lots of room gain) or a large one (with relatively little room gain).
