Can an unpublished but accepted article be used for an MSc degree?
This will depend on the conference and on local copyright laws.  I can't speak to the local laws, since I don't know what local is for you.
You may be asked to sign a copyright form, and that form will have the answer for you.  For instance, it may clearly state that the paper in its exact form is not allowed to be reproduced in any way (although I strongly doubt it would, that's a weird thing for an academic paper).  My thesis was paper-based in the sense that it contained literally the papers I wrote and had accepted, in camera-ready form.  We were allowed to do this because the various publishers considered this to be appropriate use (in fact, my copyright forms all explicitly stated that inclusion in thesis documents is acceptable).
If you are not asked to sign anything about copyright, and laws in your country agree, you retain all rights and may do whatever you want.