I don't have drm material of any type on my sandisk players so I don't worry about the precaution on the Rockbox Sansa AMS status page. http://www.rockbox.org/wiki/SansaAMS#
Installation of a bootloader may or may not cause any DRM music in the Sandisk player to suddenly expire. If it does, you may be able to fix it using these instructions
I notice that that page no longer warns against the permanent loss of drm capability. I'm guessing that means someone from Rockbox has followed the instructions in that link and they worked to allow a Rockboxed player to use drm material again. Once again, that's a guess but considering how long that page warned about the possible permanent loss of drm capability and seeing it's been changed I believe it's a good guess.