Does isolated power supplies current draw from one to another if both GNDs are connected to same circuit?
If there is no leakage from the higher voltage to the lower voltage, then no current flows between them. Each PSU sees only its own return current on its ground terminal. But you need to make sure your design guarantees that.
This mixing of voltages with a common ground is actually quite common. For example, a controller powered by 5V, running a higher-voltage higher-power motor. The motor drive part has an isolated voltage translation designed to block any leakage.