Well...does look like he could add some nice things to your mare. But as you said, these aren't exactly confo shots so its hard to judge.
Hopefully you'd get a baby with dad's pretty neck and shorter back; your mare looks quite long in the back, that's definitely her biggest flaw; very long with a long loin. The shortness I see in her neck may just be the angle of the photo, I'm not sure. And I'm sure she'll get more bulk as she fattens up. I'd love to see more pictures of her when she's back in top form (you've already done a lot with her, congratulations on that).
For all that he has a fairly short back, that stallion is a little hollow, especially for an arab. what's his age? And how has he been ridden in the past? Also, I think your mare has a better shoulder than he does.
ed. actually, I take back the short neck thing, I was looking at your older pictures again, and the length is fine. I just don't know if I'd breed a mare with that back length...but if you are going to, I think arab is a good choice. Look for one with the best back you can possibly get.