Witch Doctor- Aside from the increased healing effectiveness to your party members, I do not know if the Witch Doctor can heal himself now. I also do not know about his behavior, but judging from the way the Priests that Moloch summons, I'd say that monsters like the Witch Doctor do their best to play coward and hide behind the thing they're healing.
And yes, he does heal your Elementals. Just don't expect to see how much; I don't think they added a life bar for them (not like you'd want those covering up your screen anyway.)
Elemental Revenge/Fortitude - I am not 100% sure on the increments of Elemental Fortitude and Revenge. I think I read somewhere that they are something like 5% per skill point after level 1, but I want to say that was just a bad translation (I had to rely upon inference and Google Translator for the patch notes :-/ ).
However, I will note that the times I've partied with summoners who have used Elemental Fortitude/Revenge, their elementals IMO were a LOT stronger than they used to be. The Force Elementals are much tougher, and the toxic elementals are great little walking plague canisters!
Dominate- Dominate can be useful if you like using other monsters as weapons. It can even be used on Moloch to help kill off his priests. The downside of Dominate is that you can't hurt anything that becomes mind controlled until the mind control wears off. And of course, monsters can resist the effects of it, so multiple castings can be required if its level is too low.
The Warper- Sadly, everyone's favorite purple spinning, squeeky thing that blows stuff up took a pretty significant damage reduction. He's still a force to be reckoned with, but don't expect him to be blowing up stuff as quickly as he used to early on in the game. His HP amount is still generated randomly too, btw.
That Poison Tree-The main reason why they added the poison tree to the Summoner & Evoker's shared spell list was to give the summoner more use for focus items. And also to give more power to the yet to be added Dark Form summoner since DF uses focus items for its melee damage.
But other than that, the Poison tree can be very powerful if you decide to use it. Think of it this way - with Swarm AND Toxic Elementals.... you're pretty a nuclear waste delivery truck. And need I remind that poison did get buffed?
