Disk Warrior - Like solution for rMBP?

You don't need it for an SSD, if you have trouble with the drive it may likely be a TRIM issue usually leaving it for a lengthy time at the boot screen is sufficient to do garbage collection and thus restore performance.

Also consider third party apps as possible system causes then Activity Monitor can usually diagnose these issues.

 

DiskWarrior is used to address filesystem level problems. Has nothing to do with SSD vs HDD. Both are vulnerable to filesystem corruption due to OS bugs and the like. Defragmenting a SSD is pretty useless though.

As for the OP's question, you can boot Intel Macs off USB going back pretty much to 2005. And I believe there are newer versions of DiskWarrior available you can create a bootable USB drive with. Worst case, you can install a small copy of OS X onto a USB drive, and throw a modern copy of DiskWarrior and any other tools you want onto it. It's what I have.

 

Disk Warrior does not "de-fragment" a disk, it optimizes the directory as part of its file-system repair procedure. Run the directory graphing utility included in DW to see what is happening, or see Alsoft's HP, http://www.alsoft.com/ for the real info.
Actually an external HD combined with Carbon Copy Cloner is a much faster solution, but since you mentioned it, get a 16GB USB stick, install OS X on it, add DW and/or other utilities and use that to keep the file system on your MBP healthy.