I just called tech support at Vizio and they said it should have some line of sight, even if only peeking out from behind the sofa or chair at the soundbar. You might want to wait for an owner on this thread to address this based on experience.
Frankly, if I got one of these I would overlook the advantage of not having to run wires to the rear of the room, get long RCA cables, and put the subwoofer at the front of the room near the soundbar. I would do that because although the lower range of the sub is essentially omnidirectional, the upper end of it may generate some directional cues. Placing it at the front should provide a better, more coherent sound, IMO.