I had not heard of this so I looked it up, and personally would not do it.
Here is a link to an article. You have to scroll down a bit to get to the section about dogs. One thing mentioned in the article is that the ASPCA lists it as toxic. I checked, and they do. It can cause vomiting, diarrhea, and lethargy.
skeptoid.com/blog/2013/04/27/natural-dog-supplements-aloe-ve