I think they are. I noticed a lot of similarities on these two characters from the Unseen University: Spelter (from Sourcery) and the Senior Wrangler. The most important (and noticeable) is the physical appearance: they both do look like horses. Also Spelter is described as "wiry", and the Senior Wrangler (in the Last Continent) is described as "lightly built". They both come from a poor background, they both like long explanations (like the one when Spelter explains to Rincewind why an university can not sink). In The Last Continent one of the other wizards, when remembering the events in Sourcery, mentions that the Senior Wrangler was also there.
In the Sourcery novel, it is supposed that Spelter dies, but this is not fully clear: Death never comes for him and nobody says "Spelter is dead".
This is my theory: Spelter was sent to another dimension (maybe the Dungeon Dimensions). After a while, he managed to go back to the university ans scalated the rest of the magical levels.
The Senior Wrangler mentions in Hog Father that his name is Horace, so his full name would be Horace Spelter.
I'm sad because Pratchett doesn't make any joke about horses/the Senior Wrangler's physical appearance. It would be funny reading about the Dean pulling the Senior Wrangler's hair, and Ridcully saying "Dean, don't pull the Senior Wrangler's mane... err... hair!". :D