I am not sure if this apples to your particular problem, however I had a very similar one.
It appears that when copying files to a samba network share OS X does not lock the file, so it can be accidentally accessed by hazel while it is nt complete.
I made the following rule (and script) which appears to solve the problem.
place it as the first rule so it can ignore files in a copy state.
unfortunately I cannot explain all the xattr bits as I was unable to find the required documentation. if anyone has it please let me know

hope this helps someone

Joe
Rule:
IF
passes shell script: embedded script
DO
Ignore
the embedded script:
fb=`xattr -p com.apple.FinderInfo "$1" | awk '{print $1}' | head -n1`
if [ "$fb" == "" ]; then
fok=Y
fi
if [ "$fb" == "00" ]; then
fok=Y
fi
if [ "$fok" != "Y" ]; then
exit 0
else
exit 1
fi