A user called jbochi has converted the models to hugging face format (link), and since it’s a T5 model, ctranslate2 should support it.
But if you try to convert it using ct2-transformers-converter you’ll get an error saying that vocab and embedding sizes are not compatible. This because the tokenizer has extra tokens that are not in the model itself which was caused by incorrectly converting the sentencepiece model. I made another tokenizer and was able to convert it to ctranslate2, but the output was repeated gibberish.