I don't know why they didn't want deep striking to trigger "enters play" but that is the cleanest way in my mind to reconcile the rules.
My guess is that they want reserve cards to be "in play" so that they can interact with other card abilities and effects. If the character "enters play" when you Deep Strike, it makes it seem like the reserve card was not in play to begin with. Very confusing.
I really think the cleaner way to reconcile the rules will be to update the enslavement rules (i.e., "cards cannot enter play or be Deep Struck if they do not match your enslavement dial").
Deep strike effectively changes every rule in Initating Abilities/Deploying Cards section of the rule book. Anrankyr's ability certainly CAN deploy a units with the deep Strike and when he does, he can then use the Deep strike ability of the card to place it face down and only pay 1R.
I have to disagree with you on this one. The rules for Deep Strike are very clear that you can put cards into reserve "each round, during the deploy phase ... using a deployment turn." Even if this modifies the standard "deploy a card" use of the a player's deployment turn (instead of creating a 4th option), it does not follow that every use of the word "deploy" allows you to use the Deep Strike mechanic to put a card into reserve. If it is not during the deployment phase, and you are not using a deployment turn for the action, you are not meeting the requirements of the Deep Strike mechanic. Anrankyr can NEVER deploy a card into reserve because you are using his ability to deploy a unit, not a deployment turn -- as required by the rules for the mechanic.