Just a follow-up:
Using The Bat! 3.99.3, I have had the following compatibility issues:
With ClamWin 0.90.1.1, TBClamWin 1.01 no longer works. The plug-in loads at start-up, but virus scans fail ("The anti-virus has reported an error, the object cannot be checked for viruses").
With ClamWin 0.90.2.1, TBClamWin 1.01 will not load at start-up due to a obsolete reference to a .conf file in the ClamWin directory.
Prior to the "-nodb" ClamWin releases, TBClamWin worked fine for me.