Do I pronounce the words "de" and "deux" the same way or the vowels are different?
"en" and "an" make the same diphthong, the final 's' is silent in both cases and the 't' is silent because it's the final letter for the singular "dent"
So yes they are pronounced the same
in colloquial speech they're very similar, especially in certain dialects (though in other dialects you can definitely hear the difference). But they're still not exactly the same sound, at least not in standard French. Saying "they're the same sound" is like saying that ш and щ are the same sound. They're similar, especially to foreign ears, but they're not the same sound.
it depends on the person I think, sometimes I hear French people really make them the same but sometimes not