Thanks for the replies. I read this in Animal Sheltering magazine, in an article about how shelters and shelter vets can find good matches with one another. The article did indicate that the shelters themselves don't necessarily pay directly for the loans, but that they obtain grants that will cover that expense. And the shelters do not outright pay back 150-200k in loans, but rather will pay the monthly loan payments for as long as that person is working there.
Like I said, I haven't heard of this either, but Animal Sheltering is a very reputable magazine so I am wondering where these shelters are that do this?! And I am also hoping that this is a sign that this will become more common in the future as recognition of shelter medicine as a specialty rises.