I don't know if it will help, but not too long ago I got a list from Papa John's of Papa John's products and ingredients. This is what was given for the PJ pizza sauce:
Pizza Sauce: Vine-ripened fresh tomatoes, sunflower oil, sugar, salt, spices, garlic*, extra virgin olive oil and citric acid. *Dehydrated
The vine-ripened fresh tomatoes and citric acid leads me to believe that PJ's is using the Stanislaus tomatoes (because of the citric acid). In fact, if you go to the PJ website and look under pizza sauce, the description almost makes it certain that they are using Stanislaus. There's no one else but Escalon, possibly, that could meet PJ's tomatoes needs. The law doesn't require all of the spices to be identified so, for that, you are pretty much on your own. However, I think that it is safe to say that whatever spices they use will cater to middle of the road tastes and not include "exotic" or fancy (to most pizza eaters) ingredients. A good starting point on the herbs/spices might be a McCormick's Italian seasoning blend, or possibly Penzeys pizza seasoning. FYI, I have not been able to determine whether PJ's cooks their pizza sauces in any way. It would seem contrary to the notion of using the best and freshest ingredents.
I might add that PJ's website currently includes oregano as one of its pizza sauce ingredients, along with spices. I don't know if that means that the "spices" they use exclude herbs, or whether they are trying to put the spotlight on oregano for some reason. Most suppliers tend to distinguish between spices, herbs and seasonings/blends.
As far as using spaghetti sauces is concerned, that, again, is a matter of personal taste. Many spaghetti sauces can be on the watery side, so it may be necessary to drain them to thicken them a bit. Most supermarket brands have a lot of sugar (usually cheap corn syrup) so you might like the sweetness. Of the few brands of supermarket spaghetti sauces that I tried on pizzas--purely in the name of science, mind you--I thought the Classico brand was the best. It is not nearly as sweet as the others and, if memory serves me correct, many of their tomato-based sauces do not include corn syrup or similar sweeteners. The one that I liked best was the sundried tomato sauce.