I did a search on http://www.google.com with the parameters of ["underwater treadmill" +animal or vet] and got multiple hits...

Seems these therapy devices are becoming very popular with the Vet Universities and private practices. They have been used for many years by the equine industry for both race horse therapy and training.

Here's a link to one of the manufacturers...
Ferno site.
They list the following recent installations:
* Dover Veterinary Hospital - Durham, NH
* Oklahoma State University Vet Hospital - Stillwater, OK
* University of Tennessee - Knoxville, TN
* Alameda East Vet Clinic - Denver, CO

And an article by the American Veterinary Medical Association...
AVMA article.