Well we learn something new everyday in our glove hobby.
My thoughts. Could this be Joe Hauser who was on the Rawlings mitts in 1930? Joe was very careful about his endorsements and staying with Spalding/Reach. Brother Vince was Hutch endorser and recall that Hutch took off his first name after he left baseball and put out a DiMaggio signature glove (Vince's signature) and it has and was mistaken for a Joe D. glove. I have a James Bailey catalog somewhere and I'll check it out.
Has anyone emailed the seller, who says he welcomes questions??
Funny he's turned the mitt on it's back for the picture with no shot of the front and the "signature" of Joe.
Now, I've never heard of a Joe Dimaggio Rawlings 1b mitt in my few years in the hobby. We'll see.