[Namikaze]

That would certainly give ultrasound a good advantage.  Since ultrasound is based on echos, if someone put up a Silence spell around themselves, would the ultrasound reveal it as a big opaque ball?  Hmmm...  this might be a whole separate topic at some point, but I think it's certainly interesting to think about it.

[Kincaid]

Ultrasound has long been a common way of getting around invisibility.  And yeah, you run the risk of the Cone of Silence^TM giving away your location, so keep the diameter of the spell small so it's easier to blend into the background clutter.