''The blues are hot. They're being appreciated the way they should have been appreciated a long time ago,'' says John Lee Hooker, one of the last of the great bluesmen who came out of the rural South beginning in the '30s. This has been a good year for Hooker, 73. His duet with Bonnie Raitt on ''I'm in the Mood'' won the Grammy Award for Best Traditional Blues Recording in February. Now Hooker will be honored by a tribute concert on Oct. 16 during the Benson & Hedges Blues festival in New York City's Madison Square Garden. Among the Hooker-influenced rockers performing at the Garden will be Ry Cooder, Gregg Allman, Bo Diddley, and members of Little Feat. Bluesmen Albert Collins, Willie Dixon, and James Cotton will also play at the show, which doubles as a benefit for the Delta Blues Museum in Hooker's hometown of Clarksdale, Miss.