Veivers, 48, was sacked by the City Reds earlier this season following a turbulent off-season, and has previously served as assistant coach at Bradford and Wigan, ironically to new Reds coach Brian Noble.
The Australian, a full-back in his playing days, has been in this country since he left Queensland for St Helens back in 1984, spending 12 years at Knowsley Road and also playing for Huddersfield.
He said: "I’ve been away from the game for a few weeks, so I’m really looking forward to working with Brian and putting one over on England.
"We’ve named a strong squad, and part of my role will be to keep an eye on the players we’ve already named and those who are keen to break into it. There are plenty of outstanding players who haven’t been named and the door is still open."
McClennan last week named a 27-man squad, to be captained by Warrington's Brett Hodgson, for the game at the Halliwell Jones Stadium on Friday June 14.
Widnes will become the 16th team to feature in the Super League play-offs, having confirmed their top eight place with a win over Bradford at the weekend.