You mean to populate billing script information using a particular control panel? As to create a billing/support account out of data found in a control panel? Because Kloxo & ClientExec or WHMCS are 2 separate things. I know with WHMCS you can fetch the accounts on a cPanel/WHM server and create accounts for them on WHMCS, but I'm not so sure how it works, never done it personally.
Definitely wouldn't say so. cPanel/WHM is a much better choice, obviously, but costs you the licensing fees.
If you are looking for a good control panel cpanel like look for ISPmanager. This is actually cheap and from resselers you can get for small price if compare with cpanel. BUT! the functionality is great!
Do the thang manually Kloxo is fringe and shite thang, And don't really think there are any sort of importers for kloxo like un-finished thing.
Unfortunately you cant just migrate between Kloxo & cPanel however the process should be less painful if you let your user/client do that for you..