The dachsy will learn to play with the Boxer. How do I know, you ask? Well, I'm a professional dog trainer with 17 yrs experience that trains ALL size dogs and my Boxer, Lilly, is my Hearing Service Dog and therefore goes with me when I train. Lilly also acts as a demo dog for the owner's I'm training.
Part of my training (a large part) is play based. What does that mean? It means I use games to teach manners and behaviors. Lilly plays these training games with my clients (clients= dog(s) I'm training).
As a matter of fact, my last training graduates were from the same household/owner, trained at the same time, and their breeds were.....min pin/chi and PURE BRED DACHSY. Both of these wonderful dogs didn't get how to play with Lilly at first, but by the end of the first training session, they had gotten the idea and by the time they graduated (5 weeks later) they were old hands at "boxing".
I wouldn't worry about it. Either the Dachsy is gonna get it and play or the Dachsy is gonna say screw this and head for the hills. Remember, they are both still very young and are learning appropriate play and behavior from each other that will in turn become appropriate behaviors in your house. They are learning bite inhibition and learning about their own strength.
I do advise you to read and become familiar with the Dog Body Language stickey, as the knowledge may come in handy.
Hope this helps.
***This response is for informational purposes only. It is not meant to offend anyone.***