Seving in the Shadow Cabinet (which after all is not actually the govt) does not show a lack of integrity, depending on how it is done.
Labour's current Shadow Cabinet is a fiasco: there are people who are only in it because Corbyn was desperate. It's like a football team having to play the relatives and friends of the professionals, who've huffed off :-)
But there's a big match to be played, at least in parliament, opposing the government, and having a few big names in the side would not go amiss, as long as they don't criticise the manager too much.
Of course, what happens when the Big Game (the General Election) comes up, is another matter