Yes Billy, all wastegates and in turn wg controller or solenoids call for a pressure only source for operation to the side port and the bottom of the diaphragm for a TURBO application. Can you get away with a boost/vac source on a turbo car, sure and when using a single side port reference, you likely wont see any ill effect. Other than putting vac into the bottom of the gate when off boost.
It protects the turbo. If you develop a leak in the coldside and the gate is relying on boost from manifold to open to slow the turbo down you can easily run it up way past where it should be operating as the turbo could be throwing out 30-40psi to try and get say 15psi at the manifold to open the gate due to the leak. You would be unaware of the leak as you would still think your turbo is making your desired 15psi. When pressure is from the compressor cover itself it helps protect from a worse case scenario like this as you will see the pressure loss right away as the leak would immediately cause an observed loss of boost on your gauge run off the manifold. You would hear you turbo spool up and your gate open but not see the correct amount of boost at the manifold.
In short running the wastegate off the manifold can hide a boost leak and cause you to over spin/work the turbo and put more heat in the air and you wouldn't even know. Turbo's don't need to increase speed with rpm so controlling the turbo via gate is most optimally done with a pressure source pre intercooler where pressure and temp is highest. This effect is called boost sag on a turbo car, you get peak boost at say 3500rpms and then by 7k rpms your making 3-4psi less on your boost curve even though power and flow is the same. The turbo maintains speed and due to intercooler losses and the engine being less of a restriction at higher rpm boost "sags" in the upper rpms. Running the gate off the manifold would cause the turbo to keep accelerating with rpm to raise pressure and push more air.
This would not apply to a centri car running a gate on the coldside as blower rpm is already predetermined based on rpm and pulley size. You would want gate reference off the manifold for that setup as you are purposely making a controlled boost leak and you know boost at the manifold is less than at the compressor outlet up to the gate.