Yes, in fact, that is the default behaviour for position properties.
When an X or Y property track (or one of it parents) is set to use default result mode or explicitly relative result mode and you click on a property keyframe the value you see in the properties bar is relative.
So in a relative timeline it is common for the first keyframe to hold a value of 0 for they X and Y property tracks. 0 meaning, no changes from it's current place. The subsequent property keyframes will hold values relative to the initial one.
But I don't think you need to worry about those details.
To sum it up, if you play a timeline, the animation will be relative to the instance's current position, as long as you are using default or relative result mode.