Is this a 5V to 3.3V level converter?
The circuit can be a level converter, yes - essentially from anything above +3.3V to +3.3V + Vebo (the reverse breakdown voltage of the base-emitter junction) which is around 5V minimum according to the datasheet, so leaving some leeway, say +7.5V maximum. This circuit has a higher input impedance than the diode circuit, so if you have a weak drive this would be the better choice.   

You could replace it with the diode circuit, but remembering due to the diode drop it will only pull down to ~0.7V with silicon (probably lower due to the small current but assume the worst), I'd use a schottky diode to ensure you meet the maximum logic low level of the microcontroller input.