Yes, dogs can grieve. The symptoms you describe are common.
There are ways to ease this, more walks, more games, more attention. In general distract, distract, distract....
This might also help your poor uncle by giving him something positive to focus on.
If the problem is very extreme then a vet may be able to help with medication.
My Dad recently took in a foster who had lost both his owner and his home. He was elderly with several health issues. The prognosis was not good. He had many of the same behaviors you describe, he wouldn't eat, he howled or whined all day, paced, attempted to escape and was generally very upset.
We took turns giving the dog one on one time. I'd pop pop round after both school runs to walk him, my dad would walk him lunch time and he'd get his main evening walk with the other dogs, we hand fed him for a while, until he was eating better and he got lots of attention and hugs.
He is still with my Dad and is now a different dog, it's like he's suddenly 10 years younger 
The rescue have decided it would be unfair to separate them because of the bond they have built and the dogs age, so he is now a long term foster and will live out his remaining years with us.
Dogs can and do recover well from this.
I am sorry to hear about the loss of your Aunt 