One can analyze the OP's question two ways:
From a theoretical perspective, there is reason to conclude that shooting a .38 Special target load in a revolver chambered for .357 Magnum should display some degradation in machine accuracy. How much is uncertain.
From an experiential perspective: for many years I shot .38 target loads (2.7 grains of Bullseye pushing an H&G #51 button-nose wadcutter) out of a .357 Magnum chambered S&W revolver in the Centerfire stage of the National Gallery matches, achieving low 290s on a regular basis.
Angels on the head of a pin.