I do not think high protein is an issue for overweight dogs, more likely too much food and too little exercise, as you've already figured out. And new babies just take up so much time and energy. Dogs typically sink lower on the priority list when getting yourself showered and dressed and fed turns into a challenge! My daughter is learning that right now, poor Ellie (her dog).
You could probably just cut back on what he's currently eating and add some frozen or canned no salt green beans to bulk up the amount some. You'll see people on here also do not like Blue Buffalo products because of some dishonesty about the sources of ingredients, I believe. You could probably pick any food you want to try and just feed less of it. Most people on here do not recommend the weight management foods, just less of their regular food and more exercise. Not that my dogs are exemplars, but the 3 year old (66 lb) gets just about 2 cups of food per day and the 9 year old (86 lb) gets just a little more.
I usually feed Annamaet brand foods. Their Lean formula has 30% protein (so
not low protein) and low fat, something like 7-9%, compared to more typical 16-20% fat in "regular" food. It's not inexpensive food but they like it and do well on it. The Lean formula is also lower calorie than their other formulas but I mix the types, they don't get all Lean. I also supplement with salmon oil, so they probably get more fats than they'd get with just plain food.
The toenail issue, are you thinking SLO? A former member had a greyhound with SLO but her very informative posts on that issue were lost when the board crashed a few years ago.
I can't think of anyone else dealing with that right now, but one never knows.