Powell, 28, has not played for Wales since February and was forced to withdraw from the summer tour to New Zealand with a thigh injury.
The 2009 Lions tourist is now fully fit and back in pre-season training ahead of the new campaign and Hanks revealed a chat with former Wasps coach Gatland proved vital in the decision to sign the powerful back rower.
"I spoke to many coaches and players who have worked with Andy and the feedback was all positive," said Hanks, who is entering his second season as director of rugby at Adams Park.
"I know Warren fairly well and we had a chat. He has a lot of time for Andy and spoke very highly of him.
"Warren has been through good and bad times with him but he believes when Andy is fit and playing regular rugby he is one of the best around. He showed that by going on the Lions tour to South Africa.
"The biggest thing for Andy now is to play reasonably well. Yet people forget that he would have travelled with Wales in the summer had he not been injured.
"Selection is for Warren to decide but Dwayne Peel plays for Wales and he is in the Premiership."
Two years ago the Welsh Rugby Union stressed their desire for Welsh players to play their rugby in Wales but if Powell recaptures the kind of form he showed prior to his selection for the Lions then Gatland would be hard pushed to leave him out.
"Warren knows what we are about at Wasps and I'm sure he prefers Andy to have the chance of playing regular rugby rather than not if he had taken other options," added Hanks.
"He will be looked after well here and I'm sure that will make him available for the World Cup.
"We want to see Andy playing at the highest level and playing for Wales. He's still a young man and he could even be involved on the next Lions tour."
Powell was earmarked as the future successor to Scott Quinnell when he burst onto the senior Welsh rugby scene as a 21-year-old with Newport.
However, the colourful character struggled for consistency and almost quit the game in 2004 following unsuccessful spells at Beziers and Leicester.
He returned to rugby with Llanelli before moving to Cardiff in 2005, finally earning the first of his 14 caps against South Africa in 2008 and then traveling to the Republic with Britain and Ireland's elite six months later.