@blackop - no the controller doesn't need to be connect to the irrigation system for WiFi connectivity to work. I have my unit set up where half of the zones are phantom zones that aren't physically (or electrically) connected to anything so I can experiment with settings to see how things would work out in real life. Stating the obvious, it does need to be plugged in to a working electrical outlet.
Some WiFi tidbits from stalking the forum for a while - the unit only uses the 2.4 GHz frequency, if your WiFi router provides both 2.4 and 5 GHz channels, have different network names (SSIDs) for each frequency. As my unit is outside on the back of the property line in a storage room, I had to get a range extender for my network to push the WiFi signal that far out.
@emil mentioned a new network troubleshooting tool they have and @mckynzee has said some of support folks at Rachio assigned to networking issues read about networking for fun, so either post more details here or email email@example.com.
There are also the tips posted here -> http://support.rachio.com/article/445-how-to-activate-your-controller#tips
and 32 knowledge base articles on Gen 1 and Gen 2 WiFi here -> http://support.rachio.com/category/597-wifi-connection