Yes, employees can contribute to both a designated Roth account and a traditional, pre-tax account in the same year in any proportion they choose. The maximum amount of employee deferrals permitted for a 401(k) qualified Plan for 2011 is $16,550 if the participant is under 50 and $22,00 if the participant is over the age of 50.
Also, an employee make age-50 catch-up contributions as designated Roth contributions to his or her designated Roth account?