I would rule that he can cast spells. In my reading, the phrase "similar to a barbarian's rage" is a hint to the reader about what sort of ability he is reading. That phrase, by itself, does not have any value for the rules. Instead, the second and third sentences of the Rage ability tell you what the ability does.
(Note that I would have made a different ruling if the ability had instead had "similar to a barbarian's rage, except ..." -- in that case, you would take the existing barbarian rage ability and amend it according to the rest of the text.)