Might work, yet it doesn't kick the British out of the war, nor does it make the Americans less pro-Entent, nor does it bring food into Germany. The entire USW campaign never had enough subs to break the British materially; just the hope of breaking them morale-wise. Also keep in mind that uboats of the era didn't have the range to stay on station around Scotland/Midlands for long.I'd suggest combining no Zimmerman with a 'Sharpened' rather than Unrestricted uboat campaign would delay US entry into the war, perhaps long enough for the Kerensky offensive to fail which might further delay US entry.
The Sharpened rules are "Attacks could be made without warning on: (1) all enemy ships inside the British Isles war zone, (2) all defensively-armed enemy ships outside the war zone which would be treated as warships, (3) troop transports sailing between Le Havre and Dunkirk. All passengers ships whether armed or unarmed, inside or outside the war zone, could not be attacked by a submerged U-boat" https://www.naval-history.net/WW1NavyBritishShips-Locations10AttackedMNDate1916.htm