valve
1. The spigot is a legal connection because it has a vacuum breaker on it, but ONLY if you open and close the valve during the operation of the sprinkler system, because it is an ATMOSPHERIC vb, and not a pressure one which is required WHENEVER the water is always turned on to the valve inlets.
2. If you make a connection in the basement, then you NEED a pressure vacuum breaker/backflow preventer where you make the connection. It WILL discharge water periodically, especially when the water is turned on or off to it, or the house, so it should be in a "safe" location.