No, you can't do either of those things with the UltraDateTimeEditor. You can, however, with UltraCalendarCombo (Infragistics.Win.UltraWinSchedule):

UltraCalendarInfo calendarInfo = this.ultraCalendarCombo1.CalendarInfo;
UltraCalendarLook calendarLook = this.ultraCalendarCombo1.CalendarLook;
DateTime date = new DateTime( 2008, 7, 1 );

//  Disable a day:
Infragistics.Win.UltraWinSchedule.Day day = calendarInfo.GetDay( date, true );
day.Enabled = true;

//  Note that you can also disable a week, month, or year:
day.Week.Enabled = false;
day.Month.Enabled = false;
day.Month.Year.Enabled = false;

//  The MinDate/MaxDate properties define a contiguous range
//  of enabled dates; dates outside that range are effectively
//  disabled:
calendarInfo.MinDate = new DateTime( 2000, 1, 1 );
calendarInfo.MinDate = new DateTime( 2010, 12, 31 );

//  Change the look of a day:
DayLook dayLook = calendarLook.GetDayLook( date, true );
dayLook.Appearance.BackColor = Color.Red;