String indicators don't "convert tabs to spaces", they just display them the same because there is no way to set tab positions in string indicators (set the indicator to display "\codes", to see that tab (\t)characters are still there).
An alternative would be to use a "table" indicator. Color the grid lines with the background color if you don't want to see them. You just need a little code to turn your string into a 2D array of strings.
