Can I refreeze sauce made from frozen tomatoes
Probably. Depends on your sauce; some sauces do not tolerate freezing (e.g., they "break"). The fact that your tomatoes were frozen at one point doesn't matter.

Mostly warnings about not re-freezing foods are due to quality loss. For example, each time you freeze a vegetable, it will turn closer to mush.

Safety warnings are primarily about quick thawing (e.g., in the microwave) where the food may get into the danger zone (between 4°C–60°C/40°F–140°F); the recommendation is to cook it before freezing (if you thaw in the fridge, this is avoided). You've already got a cook step between the thaw/freeze, so even with a quick thaw method, there aren't any extra safety concerns.