Eh, not exactly.
"Subtrim" affects the servo; "trim" affects the function.
For example, in a 3-servo 120° CCPM setup, subtrimming aileron would only move that servo, resulting in a the swashplate tilting slightly toward the servo (good) yet also slightly forward (probably not good). This is because the other "aileron" servo (PITCH servo) would not be affected.
Trimming aileron would result in the swashplate tilting in the desired direction only (good) because since the function is affected, both servos would move according to your adjustment.
In a 1-servo 90° setup, such as a typical FP, either should work.