Sure they can. It's called sharing.
With all due respect, no, it doesn't. The Hinterlands either belongs to the Dalish, which is specifically what the Hero of Ferelden asks for when she explicitly states she wants the People to have their own land, or it doesn't. What you're suggesting isn't what the Dalish Hero of Ferelden asked for when she said: "I ask that land be granted to the Dalish, your majesty."
King Alistair will say, in response, that he will agree to this royal boon, publicly proclaiming: "The Hinterlands to the north of the Korcari Wilds, including Ostagar, are hereby granted to the Dalish elves." Assuming that the ultimate sacrifice was made, King Alistair will say to Keeper Marethari at the funeral: "I agree, and while I know my people cannot truly make up for what we have done to yours, I was hoping to start. I hereby offer your people the Hinterlands north of the Korcari Wilds, including Ostagar, to do with as you will."
Keeper Marethari's response is: "You would give us our own land?"
In case you were wondering, she accepts. 
Basically, it's an issue that the Dalish have their own homeland in the Hinterlands, or they don't. It's either one or the other. I think the concern is that the Hinterlands basically the same in all playthroughs, most likely due to budgetary restraints in not wanting to differentiate it simply for one specific group of fans who had their Dalish Warden chose this specific boon. I don't disagree with Palidane, and I think that it seems like the import system will show some shortcomings with issues like this.