Yes. God is one because of His simplicity (Q3 A3), infinite perfection (Q4 A2), and the ordered unity of the universe, of which universal order He is the first and sustaining cause.
Although in God there is no privation, He is known to us by way only of privation. Thus there is no reason why a certain kind of privation should not be predicated of God; for instance, that He is incorporeal and infinite; and in the same way it is said of God that He is one (i.e., undivided).