N1MM does not create a 'dupe' sheet either. ARRL will accept a Cabrillo (file or printout) as a substitute.

From the 2011 rules:
8.7. Cabrillo format log files are not required for Field Day entries. They will be accepted in lieu of
the dupe sheets but do not substitute for a summary sheet.

DXkeeper can do that export so you're all set. You still have to fill out a summary sheet but the easiest way is to use the web form and get the extra 50 points too.

Hope you had a good FD and that we (W1NY) have you in our log.

'73...
Jim/KK1W