In reading an article for my thesis, I came across an argument that goes something like this: We must avoid the two erroneous extremes of pantheism, i.e. of seeing the whole of creation as an accident of God, and Aristotelianism, i.e. seeing created beings as substances that exist in themselves without the need of a reference to a creator. I think that the second half of this statement is false. I do not believe that what the article describes as Aristotelianism is a problem, nor that it entails holding that substances do not need reference to their creator.
God is not in any of the categories. God is the cause of all being and as such is the cause of all the categories. Thus the category of substance does not entail no relationship to God as creator.
The category of substance is traditionally held to be those things that exist in themselves, while the other nine categories are accidents, i.e. those things that exists through another. It is important to realize that the categories are categories of created beings, all of which have their existence through participation in the divine esse. Thus we could truthfully say that the category of substance contains those beings who possess their limited and participated existence in themselves, while the categories of accidents contain those things that only possess their limited and participated existence through some other created things.
One need not jettison the categories to preserve God's necessary creation and sustenance of all things. One need only realize that the categories themselves are categories of created beings. That, as far as I can tell, is how St. Thomas understood it.