Yes.Vdara guests have exchange priveladges with Aria

Yes. I was actually there in February and Vdara’s pool wasn’t open yet so we were allowed to use the ones at Aria. It was a short walk and easy to get to.

Is there a charge if staying at vdara to use aria facilities

Yes, one of the great aspects of staying at Vdara is the use of the ARIA ammenities, restaurants and options.

I emailed Vdara Guest Services and asked "When staying at Vdara, can guests use the facilities at Aria?" and this is the response I received, "Vdara guests only have access to Vdara facilities complimentary as a valid room key is needed to access most pools and fitness facilities on the Las Vegas Strip."

Yes you can. They share amenities. We loved the view at Vdara!

I didn't use the pool however anything that you couldn't get at the Vdara you were offered it at Aria. Meaning, we had two free buffets offered with the booking and it was fulfilled at Aria so I think they are sister hotels, Aria has the closet casino literally across the street.

you need to ask Aria