Having consistent line of sight will definitely lead to more accurate results from our position calculation. Having said that, the impact from occlusions does become less significant as the number of anchors you are using increases. However, an environment where every device has perfect line of sight is definitely the optimal situation.
Velocity of the tag has a significantly lower impact on accuracy than does line of sight. In a good environment, the jitter in the system can definitely get down to ~10cm, but the speed at which the tag is moving is decidedly not the primary factor in determining a good environment.
Currently, we are not using any of the IMU data in our tracking computation. We plan on eventually incorporating the IMU data to help improve our performance, but it will likely be a while before that particular feature is implemented.