I have a player who is running an Untouchable in my RT game. The explorers have run into the Yu'vath dark-energy constructs before and may again soon. I'm not entirely sure what the best way to handle the interaction between the technologies, their effects and an untouchable. Since the Yu'vath use "warp energy and dark technology" I assume that some effects would be reduced or nullified by the presence of an Untouchable, but I'm not sure how all this should play out. Thoughts?

The easiest way would be to say that anything the dark energy construct uses that is psy or warp based would have no effect on the Untouchable, for example the Bone Warden fires a beam of warp energy this would have no effect on him/her. you might also say that its basic close combat attacks are deminished against him/her, like loosing its Unnatural Strength or only use 1 damage dice rather than 2.

in addition he/she would be immune to any Yu'vath influence and corruption like the one discribed in Radicals handbook page 211.

if you want to make his/her abilities even more efective you mght rule that the Dark Energy Construct gains the Daemonic Instability trait when within range of the Untouchable's Disruption radius.

some Yu'vath constructs like the Psycharus Worm (Yu'vath Halo Device) generate a Warp Field that is practically indestructable, this would liekly shut down or weaken into an ordinary force field (reduce damage by 2d10 or the like) if within range of the Disruption radius.

Finaly if you are feeling particularly generous towards the Untouchable you might rule that his/her unarmed attacks inflicts malediction on the Construct (see page 118 in DotDG).

Hope it helps or at least gives you some idears