While I'm not completly sure, the line  print "$dir exists" if ( -e $dir ); should work on all platforms. This is because of perl's unix roots, (gosh are those still showing :)
In unix, anything within the filesystem is a file, it just depends if it s a file file, a directory file, a socket file, etc. etc.

On your second question, a quick read through  perldoc File::Path leads me to beleive that your code will not work. And further read through the code, perldoc -m File::Path, leads me to believe the opposite, see Tye's post.

--SparkeyG

--Update: Corrected after reading Tye's post and further investigating the code.