Have been told that front wheel bearings are integral to the front rotors on 2009 Ford 150 and therefore can't be replaced separately. They can ONLY be replaced by replacing the entire rotor assembly. Is this correct? Sounds like BS to me, but it's a long time since I did any of this kind of work.
It isn't integral with the rotors, but the bearings are integral with the hub itself. It comes as a unit, which attaches to the steering knuckle. The rotor is separate and attaches over the lugs (wheel studs) onto the hub. You cannot change out just the bearing itself from the hub, at least they really aren't made that way. This is very common on modern day pickup trucks, as I know my '06 Silverado is setup the same basic way (I'd bet the Dodge Ram is too, but don't know for sure). To say it is common would not be out of place. I think this is probably what the person who you talked to meant, but didn't explain it very well.
Below is an image for your truck (2WD version shown - Image from RockAuto.com):