Whey from yogurt to curdle milk I know that adding acid to milk being cooked, will yield curdles that one can strain and store as cheese.

Is it possible to use the whey from my homemade yogurt (now greek-style yogurt), but instead of cooking everything in a pot, I let it sit in proofing temp for a few hours? Will I get the same result, while preserving the cultures?

The milk used for the yogurt was not cooked. The yogurt was subsequently strained over coffee filters. So I have as much whey as possible.
If you let the whey sit with the milk at proofing tempreatures (about 42 to 49 C for lactobacillicus bulgaricus, somewhat lower for bifidus, streptococcus delbrueckii and some other strains), you'll get yogurt again. 

In order to get your type of "curds" (corresponding to Russian tvorog, or German quark, or Indian paneer), you need to use acid and heat together. The yogurt whey is a good source of acid, yes. But you definitely have to follow the process as it is, including the heating.