What to do with leftover whey from vinegar-based cheese preparation
The use of vinegar in the cheese production is irrelevant. Cheese made with the acid from vinegar or cheese made with the acid from a bacterial culture should be similar.

The difference is in how high the milk was heated when the cheese was made. The albumin in milk denatures and precipitates at about boiling temperatures. If the milk was boiled before the acid was added then you are correct that there will be no ricotta.

Many quick cheeses, such as fast mozzarella, call for the milk to be warm but not boiling. You can make ricotta from that whey regardless whether the milk was acidified with bacteria or any other acid.

As for spent whey- it is very high in acid and vitamin B. You can use it in bread in place of water.

I had read of Scandinavian desserts made from condensing whey. I tried that once and found it inedible.

Roses like acidic soil. That's where most of my spent whey goes.