Are they generally pronounced with the same vowel, or not?
Yes, red and read (past tense) typically have the exact same vowel and are homophones. Pronouncing them with different vowels would be surprising, and I would expect it to occur only in a non-native accent that was influenced by the different spelling of the words. (There also apparently may be some alternative forms of the words of the words in British dialects, but I think those would rarely be encountered outside of the certain specific contexts.)