The mage guild quests do not level the skill line, so double no to your question.
The mage guild quest line has six quests and the only notable reward is two skill points at the end (for making the right choice).
The skill line levels by picking up blue lore books. a stam dk doesn't need anything in this line, but you might pick these books up when you walk by them just in case you ever respect the toon as a magic dragon knight.