Cadamarteri, who saw Allan up close in training for Dundee United, reckons the Baggies have snared a major star of the future.
The former Everton star told the Scottish Sun: "It's a great move for Scott and I think he'll do well in England.
"Most people won't know a lot about him because he's played so few games, but, having seen him in training with United, it's obvious he's a very talented boy.
"He has something special, so it's no surprise to me a Premiership club has come in for him.
"I'm maybe a bit surprised at the timing of it because I thought he might have stayed there to play in United's first-team for a while before moving on to a big club.
"But it has happened for him very early in his career and if he goes on to fulfil his potential he'll become a really top player."