This slight modification will allow your hidden sheets to appear on your userform.
wonderful code BTW.
For i = 1 To ActiveWorkbook.Worksheets.Count
Set CurrentSheet = ActiveWorkbook.Worksheets(i)
' Skip empty sheets and hidden sheets
checkme = CurrentSheet.Visible
CurrentSheet.Visible = True
If Application.CountA(CurrentSheet.Cells) <> 0 And _
CurrentSheet.Visible Then
SheetCount = SheetCount + 1
PrintDlg.CheckBoxes.Add 78, TopPos, 150, 16.5
PrintDlg.CheckBoxes(SheetCount).Text = _
CurrentSheet.Name
TopPos = TopPos + 13
End If
CurrentSheet.Visible = checkme
Next i