Again this is new for me but, here is my understanding. An inline regulator will regulate the pressure going in. If you set it at 25 psi nothing more that 25 will pass through it. The pressure relief valves do the opposite, they release pressure from the inside out at a set pressure. If the PRV is set at 25 psi and pressure inside keg gets too high it will vent out until it reaches the 25 psi again.
So if you wanted to use an inline regulator to prevent more CO2 than a set psi entering the keg that would work. However it will not vent out the keg if too much pressure is inside...for example with me, I plan to sugar prime in the sealed keg. If I had too much sugar, the excess will vent out according to my set psi.