I hear “ven“ instead of “vem“, do they sound the same?
:) So, the audio exercise I put “Ela vende o restaurante“. I hadn't listened to the slow version... :))
However, would in that case "vende o" sound more like /VEN-ji o/ than /VEN-[deh-o]/ ? (Simple characters, approximate pronunciation, not IPA or the like).
"Ven" and "vem" would indeed sound the same -- the 'n' and the 'm' are not properly pronounced, but rather indicate that the preceding vowel is nasal.
As for your second question, the answer is "yes" in most parts of Brazil, but generally "no" in other Portuguese-speaking countries.