The Dobe exepted her but now their inseperable!

Hello, me again!
 
Since my last post 'puppy trauma' things have taken a turn for the well.. different!
The dogs have exepted eachother which im so proud of my boy for doing as he's allways had problems dealing with other dogs, but now they get carried away!
I took some advice and introduced them using 'baby steps' and it really worked for me.
 
He's about 5 times bigger than her but they playfight and nip one another (especially on the ears) constantly before she finally gets tired. He being nearly 3yrs her senior keeps going and can get very annoyed with her antics! We are worried he might nip her too hard on crush her? Should they be playfighting this much? They'll share treats and rawhide bones, he'll give them to her then she'll give them back its so sweet so I dont think theres any concern for real aggression but they do get carried away playing and barking?
 
I assume it's a dominance thing and it seems as though he's trying to show her whats exeptable and whats not as when we correct her he joins in? I also assume him mouthing the back of her neck or nibbling her ears is a show of dominance too? She certainly retaliates with nips and barks, surely if she was getting hurt or scared she'd cower away? It's the first time we've had a adult dog with a pup so wanted your opinions? [:)]xxxxx