Hi Michel.
It's true that a DR550 is basically an AIX Server with TSM. There are ways to obtain root access on the system so that you can install software -- but you'll want to verify with IBM that what you're attempting will be supported.
Many years ago, I had discussions with the DR550 team about what is POSSIBLE versus what is SUPPORTED -- it was enlightening, but certainly not encouraging.
If you decide to go ahead, please don't forget to keep us in the loop!
-JD.