Yes. In Hold mode, Mountain mode or Normal Mode you should see the same mileage in any given set of driving conditions, once the car reaches the target State of Charge. (If you switch to Mountain Mode after the battery has run down and it has to push the engine harder to charge the battery back up, you'll see worse mileage for a ten or fifteen miles, until the car gets the charge up, then it'll start behaving like the others.)
The advertised MPG would be the mpg you get after the car switches from electric to gasoline like the remaining miles of a long trip without stopping to recharge the traction battery, that is not including the battery miles. Mine usually gets around 38 with all types of driving, mountain and city included.
I get the advertised EPA milage in winter. The rest of the time I get more.