Wilkinson became the 45th player to be included in Sir Clive Woodward's tour party on Sunday after coming through his third consecutive game for Newcastle unscathed.
Umaga never doubted the 25-year-old fly-half would be on the plane to New Zealand.
"I don't know whether we're too happy about him being available but that's just the way it is," Umaga said.
The All Black captain believes a squad that includes England's World Cup winner will be a very different proposition to one without Wilkinson.
"You can't deny that [he adds something to the Lions]," Umaga said.
"He is a great player, especially in pressure games - look what he did in the World Cup final.
"I'm not going to say that it's going to be like a World Cup final but the intensity is going to be right up there."
Wilkinson has not played international rugby since the final in Sydney in 2003 because of a succession of injuries but the All Blacks skipper expects the Englishman to thrive on his return to the big time.
"Looking at the two sides, I don't think there is going to be much between them and with a person that's done it before on the biggest stage in the world, it's going to be right up his alley."
It will be Wilkinson's second Lions tour after playing under Graham Henry, now the coach of New Zealand, in 2001, but he faces stiff competition for the number 10 Test jersey from Wales' Stephen Jones, Ireland's Ronan O'Gara and fellow countryman Charlie Hodgson.