Well, yes. Any debate on the matter would be a bit silly - "Hmm, here Death refers to Rincewind as 'bloke'. Maybe 'Bloke' is Rincewind's first name?"

Given that Rincewind was in the original books, which were satires of the then state of the fantasy genre, I think it's fairly obvious that Rincewind is only supposed to have one name, as usual for such a character. Just as Hrun (or Cohen) the Barbarian only has one name and an appellation, so does Rincewind the Wizzard.