Tested in JDK1.2Beta4-E.

Run javadoc command with custom doclets using option -doclet, error exit status from doclets is not reflected by javadoc:

$ javadoc -doclet Test Test.java
Loading source file Test.java...
Constructing Javadoc information...

$ echo $?
0

$ more Test.java
import com.sun.javadoc.*;

public class Test extends Doclet {
  
  public static boolean start(RootDoc root) {
    return false;
  }
}
$