If selected against Yeovil Town at Huish Park this afternoon the central defensive pair will each make their 100th appearance in a Blackburn Rovers shirt.
Jason Lowe and David Dunn also made their 100th and 350th appearances recently, with Dann and Hanley the latest to reach a coveted landmark.
"I think in terms of their importance to the football club they've been massive," said Bowyer.
"They've forged a hell of a partnership last season, Scott was bought for a lot of money and I think he's certainly justified that.
"He's become the captain since he's come here and he has got better and better with every game.
"I can't speak highly of him enough, he trains every day and is a real top pro.
"Grant, he's someone I've known for 5-6 years now and he's another who has just got better and better.
"We're delighted that he's a full international with the Scotland team now and hopefully he is going to be a player here for a long, long time.
"I'm delighted with his progress and delighted that he is making his 100th appearance for the club.
"We just need them both to start scoring goals. They had a competition between them last season which Dann won 5-3.
"We need the pair to start that again because neither has scored yet."
Tickets for the Yeovil Town match this afternoon will be on sale from Huish Park. Prices are from £22 Adults, £17 Seniors, £15 16-21s and £1 Juniors Under 16s.