Count Not Equal
If inicijaliDT is a one-column range, you can do one of the following:
Sub testLoop()
    Dim cel As Range
    Dim brojRedaka As Long
    inicijali = wsNOSTROSheet.Range("R" & brojac).Value
    For Each cel In inicijaliDT.Cells
        If cel.Value <> inicijali Then
            brojRedaka = brojRedaka + 1
        End If
    Next cel
    'Debug.Print brojRedaka
End Sub
Sub testCountIf()
    Dim brojRedaka As Long
    inicijali = wsNOSTROSheet.Range("R" & brojac).Value
    brojRedaka = inicijaliDT.Rows.Count _
        - Application.CountIf(inicijaliDT, inicijali)
    'Debug.Print brojRedaka
End Sub
If inicijaliDT is a multi-column range and you are trying to count the number of rows where inicijali is not found in any of their cells, you can do one of the following:
Sub testRowLoop()
    Dim RowRange As Range
    Dim cel As Range
    Dim brojRedaka As Long
    Dim isFound As Boolean
    inicijali = wsNOSTROSheet.Range("R" & brojac).Value
    For Each RowRange In inicijaliDT.Rows
        For Each cel In RowRange.Cells
            If cel.Value = inicijali Then
                isFound = True
                Exit For
            End If
        Next cel
        If isFound Then
            isFound = False
        Else
            brojRedaka = brojRedaka + 1
        End If
    Next RowRange
    'Debug.Print brojRedaka
End Sub
Sub testRowMatch()
    Dim RowRange As Range
    Dim brojRedaka As Long
    inicijali = wsNOSTROSheet.Range("R" & brojac).Value
    For Each RowRange In inicijaliDT.Rows
        If IsError(Application.Match(inicijali, RowRange, 0)) Then
            brojRedaka = brojRedaka + 1
        End If
    Next RowRange
    ' Debug.Print brojRedaka
End Sub