is soul bond considered an ability.
For example
{Naya Hushblade} has shroud, soul bond never says target so can you soul bond a {lightning marauder} with her?
It is an ability that does not target. Besides the fact that it doesn't say target in the reminder text, this was the best ruling I could find:
702.94b (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=702.94b):
702.94c When the soulbond ability resolves, if either object that would be paired is no longer a creature, no longer on the battlefield, or no longer under the control of the player who controls the soulbond ability, neither object becomes paired.
Neither soulbond ability targets any creature.
For reference, the two abilities huntertay mentions:
702.94a (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=702.94a): Soulbond is a keyword that represents two triggered abilities. "Soulbond" means "When this creature enters the battlefield, if you control both this creature and another creature and both are unpaired, you may pair this creature with another unpaired creature you control for as long as both remain creatures on the battlefield under your control" and "Whenever another creature enters the battlefield under your control, if you control both that creature and this one and both are unpaired, you may pair that creature with this creature for as long as both remain creatures on the battlefield under your control."