The Vedas refer to not 33 crore Devatas but 33 types (Koti in Sanskrit) of Devatas. They are explained in Shatpath Brahman and many other scriptures very clearly.
In Brhadaranyaka Upanishad while discussing Brahman, Yajnavalkya is asked how many gods are there. He says that there are three hundred and three and three thousand and three gods. When the question is repeated? He says, thirty three. When the question is again repeated he says, six. Finally, after several repetitions he says ONE. (Chapter I, hymn 9, verse 1)
The number 33 comes from the number of Vedic gods explained by Yajnavalkya in Brhadaranyaka Upanishad – the eight Vasus, the eleven Rudras, the twelve Adityas, Indra and Prajapati. (Chapter I, hymn 9, verse 2)