It’s possible to use in air, but you’ll need to turn on debug mode to be able to set the speed of sound to an appropriate value for air (outside of debug mode Ping Viewer restricts the speed of sound to values that make sense for water).
In water, yes. In air the minimum detectable distance is more like 35 cm.
The technical details outline the supported serial baud rates, the message protocol, the message subsets from the protocol, and link the three different code library implementations that allow you to construct, send, and receive Ping messages:
If you’re wanting to send messages directly (via your own program instead of Ping Viewer) then I’d recommend using one of the provided libraries 
Given it’s working in Ping Viewer, the connections should be fine