IMHO, yes and no.
Leone was setting the foundation to what was to become the quintessential spaqhetti western formula: "The lone gunman in pursuit of money to the exclusion of all else". So Eastwood could be playing the same guy, but I think it's more like he's playing the same type of guy, he was just so perfect for that/those role(s) that Leone would have been crazy not to exploit it. Same thing with Lee Van Cleef as a bad guy, he was in the last 2 films in the No Name trilogy (It's also known as the "Dollars Trilogy", even though the last* film, Good/Bad/Ugly, doesn't have the word "dollars" in the title, it's still about a guy after money) and he played different roles, he's so awesome in "A Few Dollars More"!!!
I'm pretty positive "Blondie" is Tuco's nickname for Eastwood's character in GBU, as for Joe/Joe Manco, I dunno.
*The only thing, IMHO, that could tie the 3 roles together as the same character is the poncho (and maybe the cigar smoking ). Eastwood is wearing the same poncho in the first 2 films but he isn't in The Good, The Bad and The Ugly... at first. He picks it up near a dying soldier just before the cemetary/final shoot out scene, so in a way, this film is actually a prequel to the first 2 $ films.
"My mule don't like people laughing" - Man With No Name