Cargo stations are only needed if your line is picking up goods at the station, so running freight into a passenger station is fine as long as you're only making deliveries. If you build a separate cargo station within catchment of the passenger station, you can also transfer cargo from lines dropping off at the passenger station to lines picking up at the freight station, but not vice versa.

Note that this also works for other modes of transportation - perhaps most usefully, trucks and on-street bus stops.

Thank you!