depends on the sensory input and scanners the Magnaguard has, as a bodyguard I would assume it would be a detector in which case it would be even, the winner would be who got the lucky hit in first.
most Dark Templar have about the same level of weapons skill as a Jedi Knight, so the fight is pretty even
a Zealot woulden't last very long, a Hero by default would win because of their skill, and of course a Hero isnt skilled because he/she/it is a hero, it's a Hero because it is so skilled!