Shadowdancer shadow companions have the following text:
At 3rd level, a shadowdancer can summon a shadow, an undead shade. Unlike a normal shadow, this shadow's alignment matches that of the shadowdancer, and the creature cannot create spawn. The summoned shadow receives a +4 bonus on Will saves made to halve the damage from positive channeled energy and the shadow cannot be turned or commanded. This shadow serves as a companion to the shadowdancer and can communicate intelligibly with the shadowdancer. This shadow has a number of hit points equal to half the shadowdancer's total. The shadow uses the shadowdancer's base attack bonus and base save bonuses.
If a shadow companion is destroyed, or the shadowdancer chooses to dismiss it, the shadowdancer must attempt a DC 15 Fortitude save. If the saving throw fails, the shadowdancer gains one permanent negative level. A successful saving throw avoids this negative level. A destroyed or dismissed shadow companion cannot be replaced for 30 days.
Grave Knights have the following special ability:
As a standard action, a graveknight can attempt to bend any undead creature within 50 feet to its will. The targeted undead must succeed at a Will save or fall under the graveknight's control. This control is permanent for unintelligent undead; an undead with an Intelligence score is allowed an additional save every day to break free from the graveknight's control. A creature that successfully saves cannot be affected again by the same graveknight's undead mastery for 24 hours. A graveknight can control 5 Hit Dice of undead creatures for every Hit Die it has. If the graveknight exceeds this number, the excess from earlier uses of the ability becomes uncontrolled, as per animate dead.
Which takes precedence?
I'm voting for the Shadowdancer.
Also, thank you for specifically posting the text.
Immune is immune. Not much more to say.
Other abilites usually specificly say when they circumvent things like that.