Symantec don't seem to distribute LUDBFIX any longer, but someone was kind enough to send me a copy of LUDBFIX from a previous support incident of theirs. In examining the file, and comparing it with the DBVALIDATOR tool, I noticed that both of these seem to use the same underlying Java code called 'ludbfix'.
LUDBFIX proper runs LUDBFIX.Main
DBVALIDATOR runs LUDBFIX.XMLValidator
At least, on SEPM v11 MR2 this is the case. I experimented and made a copy of the DBVALIDATOR batch file in the Tools directory, and I called it LUDBFIX.BAT and edited it to replace the call to "XMLValidator" with a call to "Main".
When I ran it, it indeed seemed to run LUDBFIX and it put a file in the \Log directory named something like LUDBFIX.LOG (not sure now of the exact name).
This is obviously a hack of what Symantec intended. It may be dangerous. It may damage your database (although it didn't seem to damage mine on my MR2 installation when I tried it). So I cannot recommend that anyone try it ...
UNLESS ...
you are desperate. I was, as I had a corrupted database and was trying everything I could to try to fix it, because the alternative was to reinstall. So maybe, as a last resort, this may help someone.
Incidentally, even though this didn't fix my problems with the database, I found a solution later by installing MR4 and then MR4 MP2 over the top of my MR2 installation. This seemed to fix my database corruption issues. So perhaps this is the best path to follow, rather than hacking Symantec's database validation tools!