The rules for these have been released.
Per the forums at BOLS
-pick a unit from the formation close to the captain,that unit can fire in the movement phase instead of moving (and then can still fire in the shooting phase)
-pick an enemy unit within 18" of the dominus and within his LoS at the start of the shooting phase,all units from the formation repeat to hit against that unit for that phase
-if the gargoyle are close to the Tyrant during the movement phase,you can immediatly remove them from the game and place them back in the same turn coming from deep strike.If they DS close to the warrior unit from the formation,they dont scatter
-when the scarabs and warrior units from the formation are destroyed,you place them back in game close to the overlord at the start of the next turn
-All infantry has 4+ cover while standing near the LR
-Pick a unit close to the ethereal,remove all the models of that unit save for one,then redeply all those models keeping cohesion with the model you left on the field.Not sure how often/when you can do it
I did hear from someone who has his hands on the AdMech one already and confirmed that it's legit for at least that one.