Waveguide surrounds can work quite well but there are some caveats related to placement. First, they will have a fairly narrow vertical dispersion and this can be an issue if you want to cover a bunch of seats and the surrounds are close to some of the seats. I would want meet the following criteria:
1. You have at least 20" between the side wall and nearest seat.
2. The ability to place the surround high on the wall and angle it down.
3. Wide vertical nulls based on the crossover design and driver placement.
If you can do this, then it will work quite well. If you can't meet those requirements I'd suggest something like a pro coax or typical dome setup.
If you are sketchup handy, you can mock up your room and draw out the coverage pattern of the horn and how it will cover your seats based on different placements. I would estimate a vertical pattern of about 40 deg for the SEOS since there is some narrowing in the vertical.
I'd also suggest using something like a SEOS-12 and 10" woofer combination instead of a 12 or 15" woofer because it will give you a closer CTC spacing and allow for wider null angles with the same crossover point. Something like Bwaslo's recent design in the SEOS thread might work well since it is a 10" woofer and a 1200hz crossover. That should space the nulls very wide which is more important in a surround than in a LCR speaker.