Neither MakeMKV nor the DASPI installer have been digitally signed for Mountain Lion (as of 2012/08/18).
Thus, if you try to launch it directly, Mac OS X will tell you that it can't launch it. The workaround is easy though:
1) locate the file in Finder (e.g. MakeMKV.app in /Applications)
2) right-click (or ctrl-click) on the application, and choose open
3) in the dialog that appears, choose open
4) enjoy!