just a basic question...do servos (not continuous rotation) have a fixed "home" point which they use as a reference point? For example, if i moved the servo arm 30 degrees to the right, then used the command:
would the servo arm move another 60 degrees (for a total of 90), or would it move an extra 90 degrees (for a total of 120)?
No there is no default start-up position you can assume, therefore no relative positioning capabilities.
You should keep a variable in your sketch that saves the last commanded position you outputted, from that you can do either absolute or relative positioning dependent on you sketch programming.
The servo write commands (using degrees) sets the end points of total range of travel. There is no 'default position' as the servo on first powering up just starts reading the command signal and moves to that absolute position.